Improve perf of Graph.Scope.scopeFor hotspot (#9620)

`scopeFor` appears to be a hotspot of the compiler. By choosing a more suitable data structure that indexes on the occurrence's id we seem to gain about 25% on some benchmarks. Quick win.

Related to #9235.

# Important Notes
Local benchmark runs of `org.enso.compiler.benchmarks.module.ManyLocalVarsBenchmark.longMethodWithLotOfLocalVars
`
Before
```
[info] # Warmup Iteration   1: 61.638 ms/op
[info] # Warmup Iteration   2: 49.224 ms/op
[info] # Warmup Iteration   3: 47.341 ms/op
[info] # Warmup Iteration   4: 46.946 ms/op
[info] # Warmup Iteration   5: 46.901 ms/op
[info] # Warmup Iteration   6: 49.536 ms/op
[info] Iteration   1: 50.438 ms/op
[info] Iteration   2: 47.326 ms/op
[info] Iteration   3: 46.917 ms/op
[info] Iteration   4: 45.824 ms/op
```

After
```
[info] # Warmup Iteration   1: 86.493 ms/op
[info] # Warmup Iteration   2: 36.084 ms/op
[info] # Warmup Iteration   3: 32.588 ms/op
[info] # Warmup Iteration   4: 33.895 ms/op
[info] # Warmup Iteration   5: 31.986 ms/op
[info] # Warmup Iteration   6: 31.236 ms/op
[info] Iteration   1: 31.258 ms/op
[info] Iteration   2: 31.673 ms/op
[info] Iteration   3: 30.931 ms/op
[info] Iteration   4: 30.902 ms/op
```

engine/runtime-compiler/src/main/java/org/enso/compiler/pass/analyse/PassPersistance.java

@@ -24,6 +24,7 @@ import org.enso.persist.Persistable;
 import org.enso.persist.Persistance;
 import org.openide.util.lookup.ServiceProvider;
 import scala.Option;
+import scala.Tuple2$;
 
 @Persistable(clazz = CachePreferenceAnalysis.WeightInfo.class, id = 1111)
 @Persistable(clazz = DataflowAnalysis.DependencyInfo.class, id = 1112)
@@ -128,7 +129,8 @@ public final class PassPersistance {
     @SuppressWarnings("unchecked")
     protected Graph.Scope readObject(Input in) throws IOException {
       var childScopes = in.readInline(scala.collection.immutable.List.class);
-      var occurrences = (scala.collection.immutable.Set) in.readObject();
+      var occurrencesValues = (scala.collection.immutable.Set<Graph.Occurrence>) in.readObject();
+      var occurrences = occurrencesValues.map(v -> Tuple2$.MODULE$.apply(v.id(), v)).toMap(null);
       var allDefinitions = in.readInline(scala.collection.immutable.List.class);
       var parent = new Graph.Scope(childScopes, occurrences, allDefinitions);
       var optionParent = Option.apply(parent);
@@ -145,7 +147,7 @@ public final class PassPersistance {
     @SuppressWarnings("unchecked")
     protected void writeObject(Graph.Scope obj, Output out) throws IOException {
       out.writeInline(scala.collection.immutable.List.class, obj.childScopes());
-      out.writeObject(obj.occurrences());
+      out.writeObject(obj.occurrences().values().toSet());
       out.writeInline(scala.collection.immutable.List.class, obj.allDefinitions());
     }
   }

engine/runtime-compiler/src/main/scala/org/enso/compiler/context/LocalScope.scala

@@ -140,10 +140,10 @@ class LocalScope(
       .getOrElse(Map())
 
     scope.occurrences.foreach {
-      case x: AliasGraph.Occurrence.Def =>
+      case (id, x: AliasGraph.Occurrence.Def) =>
         parentResult += x.symbol -> new FramePointer(
           level,
-          allFrameSlotIdxs(x.id)
+          allFrameSlotIdxs(id)
         )
       case _ =>
     }

engine/runtime-compiler/src/main/scala/org/enso/compiler/pass/analyse/AliasAnalysis.scala

@@ -602,12 +602,12 @@ case object AliasAnalysis extends IRPass {
               )
             )
         } else {
-          val f = scope.occurrences.collectFirst {
+          val f = scope.occurrences.values.collectFirst {
             case x if x.symbol == name.name => x
           }
           arg
             .copy(
-              ascribedType = Some(new Redefined.Arg(name, arg.location))
+              ascribedType = Some(Redefined.Arg(name, arg.location))
             )
             .updateMetadata(
               new MetadataPair(

engine/runtime-compiler/src/main/scala/org/enso/compiler/pass/analyse/alias/Graph.scala

@@ -272,11 +272,11 @@ sealed class Graph extends Serializable {
     def getShadowedIds(
       scope: Graph.Scope
     ): Set[Graph.Occurrence] = {
-      scope.occurrences.collect {
+      scope.occurrences.values.collect {
         case d: Occurrence.Def if d.symbol == definition.symbol    => d
         case g: Occurrence.Global if g.symbol == definition.symbol => g
       } ++ scope.parent.map(getShadowedIds).getOrElse(Set())
-    }
+    }.toSet
 
     definition match {
       case d: Occurrence.Def =>
@@ -343,13 +343,13 @@ object Graph {
   /** A representation of a local scope in Enso.
     *
     * @param childScopes all scopes that are _direct_ children of `this`
-    * @param occurrences all symbol occurrences in `this` scope
+    * @param occurrences all symbol occurrences in `this` scope indexed by the identifier of the name
     * @param allDefinitions all definitions in this scope, including synthetic ones.
     *                       Note that there may not be a link for all these definitions.
     */
   sealed class Scope(
     var childScopes: List[Scope]             = List(),
-    var occurrences: Set[Occurrence]         = Set(),
+    var occurrences: Map[Id, Occurrence]     = HashMap(),
     var allDefinitions: List[Occurrence.Def] = List()
   ) extends Serializable {
 
@@ -437,7 +437,13 @@ object Graph {
       * @param occurrence the occurrence to add
       */
     def add(occurrence: Occurrence): Unit = {
-      occurrences += occurrence
+      if (occurrences.contains(occurrence.id)) {
+        throw new CompilerError(
+          s"Multiple occurrences found for ID ${occurrence.id}."
+        )
+      } else {
+        occurrences += ((occurrence.id, occurrence))
+      }
     }
 
     /** Adds a definition, including a definition with synthetic name, without
@@ -456,7 +462,7 @@ object Graph {
       * @return the occurrence for `id`, if it exists
       */
     def getOccurrence(id: Graph.Id): Option[Occurrence] = {
-      occurrences.find(o => o.id == id)
+      occurrences.get(id)
     }
 
     /** Finds any occurrences for the provided symbol in the current scope, if
@@ -469,9 +475,9 @@ object Graph {
     def getOccurrences[T <: Occurrence: ClassTag](
       symbol: Graph.Symbol
     ): Set[Occurrence] = {
-      occurrences.collect {
+      occurrences.values.collect {
         case o: T if o.symbol == symbol => o
-      }
+      }.toSet
     }
 
     /** Unsafely gets the occurrence for the provided ID in the current scope.
@@ -496,7 +502,9 @@ object Graph {
     def hasSymbolOccurrenceAs[T <: Occurrence: ClassTag](
       symbol: Graph.Symbol
     ): Boolean = {
-      occurrences.collect { case x: T if x.symbol == symbol => x }.nonEmpty
+      occurrences.values.collectFirst {
+        case x: T if x.symbol == symbol => x
+      }.nonEmpty
     }
 
     /** Resolves usages of symbols into links where possible, creating an edge
@@ -511,7 +519,7 @@ object Graph {
       occurrence: Graph.Occurrence.Use,
       parentCounter: Int = 0
     ): Option[Graph.Link] = {
-      val definition = occurrences.find {
+      val definition = occurrences.values.find {
         case Graph.Occurrence.Def(_, name, _, _, _) =>
           name == occurrence.symbol
         case _ => false
@@ -530,7 +538,7 @@ object Graph {
       * @return a string representation of `this`
       */
     override def toString: String =
-      s"Scope(occurrences = $occurrences, childScopes = $childScopes)"
+      s"Scope(occurrences = ${occurrences.values}, childScopes = $childScopes)"
 
     /** Counts the number of scopes in this scope.
       *
@@ -555,9 +563,7 @@ object Graph {
       * @return the scope where `id` occurs
       */
     def scopeFor(id: Graph.Id): Option[Scope] = {
-      val possibleCandidates = occurrences.filter(o => o.id == id)
-
-      if (possibleCandidates.isEmpty) {
+      if (!occurrences.contains(id)) {
         if (childScopes.isEmpty) {
           None
         } else {
@@ -584,10 +590,8 @@ object Graph {
             Some(childCandidate)
           }
         }
-      } else if (possibleCandidates.size == 1) {
-        Some(this)
       } else {
-        throw new CompilerError(s"Multiple occurrences found for ID $id.")
+        Some(this)
       }
     }
 
@@ -629,7 +633,7 @@ object Graph {
       * @return the set of symbols
       */
     def symbols: Set[Graph.Symbol] = {
-      val symbolsInThis        = occurrences.map(_.symbol)
+      val symbolsInThis        = occurrences.values.map(_.symbol).toSet
       val symbolsInChildScopes = childScopes.flatMap(_.symbols)
 
       symbolsInThis ++ symbolsInChildScopes