Make sure import/export resolution does not bring duplicates (#4037)

Component Groups may add additional modules to compilation. This change ensures that whatever modules result from import/export resolution, they are not duplicate. Not only could that lead to unnecessary compilation but also to multiple reports of the same error which would be confusing to users.
This fixes https://www.pivotaltracker.com/story/show/184189980

# Important Notes
No easy way to write unit tests for this, so skipping that on purpose for now.

engine/runtime/src/main/scala/org/enso/compiler/Compiler.scala

@@ -256,7 +256,7 @@ class Compiler(
       } else {
         modules
       }
-    }
+    }.distinct
 
     var hasInvalidModuleRelink = false
     if (irCachingEnabled) {