[Frontend] Swift 6: Enable checked continuations when suspending for an async ObjC calls

Enables `-checked-async-objc-bridging` flag by default starting
from swift 6 language mode to provide enhanced debugging and
runtime checking for the correct usage of continuations passed
in a call to ObjC from Swift.

lib/Frontend/CompilerInvocation.cpp

@@ -1572,6 +1572,8 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
                      A->getAsString(Args), A->getValue());
       HadError = true;
     }
+  } else if (Opts.isSwiftVersionAtLeast(6)) {
+    Opts.UseCheckedAsyncObjCBridging = true;
   }
 
   Opts.DisableDynamicActorIsolation |=