Field promotion: allow super.property to be promoted.

Fixes test language/inference_update_2/field_invocation_promotion_test
on front end configurations.

Note that there is still an outstanding problem with `this.property`
and `super.property` getting treated as synonymous
(dart-lang/sdk#50138).  That will be
addressed in a later CL.

Bug: dart-lang/language#2020
Change-Id: Idb95601b47711df5ca7517c83621638783446e45
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/269743
Reviewed-by: Johnni Winther <[email protected]>
Commit-Queue: Paul Berry <[email protected]>

pkg/front_end/lib/src/fasta/type_inference/inference_visitor_base.dart

@@ -3387,8 +3387,9 @@ abstract class InferenceVisitorBase implements InferenceVisitor {
     if (member is Procedure && member.kind == ProcedureKind.Method) {
       return instantiateTearOff(inferredType, typeContext, expression);
     }
-    flowAnalysis.thisOrSuperPropertyGet(
-        expression, name.text, member, inferredType);
+    inferredType = flowAnalysis.thisOrSuperPropertyGet(
+            expression, name.text, member, inferredType) ??
+        inferredType;
     return new ExpressionInferenceResult(inferredType, expression);
   }