[CSSimplify] Allow .callAsFunction injection after constructor in diagnostic mode

If argument matching fails in diagnostic mode, it can only mean
that it couldn't find any viable fixes to attempt, so let's try
injecting `.callAsFunction` when appropriate to help diagnose
possible mismatches related to ambiguous syntax.

Author: xedin

lib/Sema/CSSimplify.cpp

@@ -10674,9 +10674,6 @@ ConstraintSystem::simplifyApplicableFnConstraint(
 
     switch (matchCallResult) {
     case SolutionKind::Error: {
-      if (shouldAttemptFixes())
-        return SolutionKind::Error;
-
       auto resultTy = func2->getResult();
 
       // If this is a call that constructs a callable type with