don't implicitly close transclude blocks

fixes #4592

unison-src/transcripts/fix4592.md

@@ -1,8 +1,8 @@
 ```ucm:hide
-.> builtins.merge
+.> builtins.mergeio
 ```
 
-```unison:error
+```unison
 doc = {{ {{ bug "bug"
   52 }} }}
 ```

unison-src/transcripts/fix4592.output.md

@@ -7,9 +7,12 @@ doc = {{ {{ bug "bug"
 
   Loading changes detected in scratch.u.
 
-  I found a closing '}}' here without a matching 'syntax.docTransclude'.
-  
-      2 |   52 }} }}
+  I found and typechecked these definitions in scratch.u. If you
+  do an `add` or `update`, here's how your codebase would
+  change:
   
+    ⍟ These new definitions are ok to `add`:
+    
+      doc : Doc2
 
 ```

unison-syntax/src/Unison/Syntax/Lexer.hs

@@ -258,7 +258,7 @@ token'' tok p = do
     topHasClosePair :: Layout -> Bool
     topHasClosePair [] = False
     topHasClosePair ((name, _) : _) =
-      name `elem` ["{", "(", "[", "handle", "match", "if", "then"]
+      name `elem` ["syntax.docTransclude", "{", "(", "[", "handle", "match", "if", "then"]
 
 showErrorFancy :: (P.ShowErrorComponent e) => P.ErrorFancy e -> String
 showErrorFancy (P.ErrorFail msg) = msg