Add missing import prefix to FUNCTION

This is a commit that should have been part of 340181.

Change-Id: Ic87c9d4975f0b9504395e6bfdac9b3c22fbcddd6
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/340082
Reviewed-by: William Hesse <whesse@google.com>
Commit-Queue: Erik Ernst <eernst@google.com>

tools/spec_parser/Dart.g

@@ -1185,7 +1185,7 @@ patternField
     ;
 
 objectPattern
-    :    (typeName typeArguments? | FUNCTION) '(' patternFields? ')'
+    :    (typeName typeArguments? | typeNamedFunction) '(' patternFields? ')'
     ;
 
 patternVariableDeclaration
@@ -1439,9 +1439,13 @@ typeNotFunction
     |    VOID
     ;
 
+typeNamedFunction
+    :    (typeIdentifier '.')? FUNCTION
+    ;
+
 typeNotVoidNotFunction
     :    typeName typeArguments?
-    |    (typeIdentifier '.')? FUNCTION
+    |    typeNamedFunction
     ;
 
 typeName