[Diagnostics] Use ContextualFailure and ContextualMistatch as base classes

for `AutoClosurePointerConversionFailure` and `AllowAutoClosurePointerConversion`
respectively.

lib/Sema/CSFix.cpp

@@ -271,7 +271,7 @@ AutoClosureForwarding *AutoClosureForwarding::create(ConstraintSystem &cs,
 
 bool AllowAutoClosurePointerConversion::diagnose(Expr *root, bool asNote) const {
   auto failure = AutoClosurePointerConversionFailure(root, getConstraintSystem(),
-      PointeeType, PointerType, getLocator());
+      getFromType(), getToType(), getLocator());
   return failure.diagnose(asNote);
 }