[Concurrency] Actor-isolated members cannot satisfy protocol requirements.

Enforce the actor-isolation constraint that an actor-isolated member
(e.g., a non-async instance method or an instance property) cannot be
used to conform to a protocol requirement.

lib/Sema/MiscDiagnostics.cpp

@@ -17,6 +17,7 @@
 #include "MiscDiagnostics.h"
 #include "ConstraintSystem.h"
 #include "TypeCheckAvailability.h"
+#include "TypeCheckConcurrency.h"
 #include "TypeChecker.h"
 #include "swift/AST/ASTWalker.h"
 #include "swift/AST/NameLookup.h"