[Diagnostics] Improve the diagnostics for invalid type access on an

existential type in expression context.

Author: hborla

lib/Sema/CSDiagnostics.cpp

@@ -4297,7 +4297,8 @@ bool AllowTypeOrInstanceMemberFailure::diagnoseAsError() {
     }
   }
 
-  if (BaseType->is<AnyMetatypeType>() && !Member->isStatic()) {
+  bool isStaticOrTypeMember = Member->isStatic() || isa<TypeDecl>(Member);
+  if (BaseType->is<AnyMetatypeType>() && !isStaticOrTypeMember) {
     auto instanceTy = BaseType;
 
     if (auto *AMT = instanceTy->getAs<AnyMetatypeType>()) {

test/decl/typealias/protocol.swift

@@ -190,6 +190,9 @@ struct T5 : P5 {
   var v8 = P6.A.self
   var v9 = P6.B.self // expected-error {{cannot access type alias 'B' from 'P6'; use a concrete type or generic parameter base instead}}
 
+  var v10 = (any P6).A.self
+  var v11 = (any P6).B.self // expected-error {{cannot access type alias 'B' from 'any P6'; use a concrete type or generic parameter base instead}}
+
   struct Generic<T> {
     func okay(value: T.A) where T == any P6 {}