Elements. Use FormalParameterFragmentImpl instead of ParameterElementMixin in InstanceMemberInferrer.

Of course eventually we should use FormalParameterElementImpl here,
but for now my goal is to get rid of `ParameterElementMixin`, and
untangle Member(s).

Change-Id: Icbc8c400d9cc49e69d67274c422f757b61e8b52a
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/437903
Reviewed-by: Paul Berry <[email protected]>
Commit-Queue: Konstantin Shcheglov <[email protected]>

Author: scheglov

pkg/analyzer/lib/src/summary2/instance_member_inferrer.dart

@@ -58,7 +58,7 @@ class InstanceMemberInferrer {
   /// given [parameter]. If the parameter is positional, then it appears at the
   /// given [index] in its enclosing element's list of parameters.
   FormalParameterElementMixin? _getCorrespondingParameter(
-    ParameterElementMixin parameter,
+    FormalParameterFragmentImpl parameter,
     int index,
     List<FormalParameterElementMixin> methodParameters,
   ) {