[CSSimplify] Determine whether type is know Foundation entity in a safer way

Instead of trying to get string representation of the type itself,
let's just get it based on the type name, which works well with the
list of types we have.

Resolves: rdar://113675093
(cherry picked from commit b83a73d)

Author: xedin

lib/Sema/CSSimplify.cpp

@@ -2761,10 +2761,17 @@ assessRequirementFailureImpact(ConstraintSystem &cs, Type requirementType,
   if (locator.isForRequirement(RequirementKind::Conformance)) {
     // Increase the impact of a conformance fix for a standard library
     // or foundation type, as it's unlikely to be a good suggestion.
-    if (resolvedTy->isStdlibType() ||
-        getKnownFoundationEntity(resolvedTy->getString())) {
-      impact += 2;
+    {
+      if (resolvedTy->isStdlibType()) {
+        impact += 2;
+      }
+
+      if (auto *NTD = resolvedTy->getAnyNominal()) {
+        if (getKnownFoundationEntity(NTD->getNameStr()))
+          impact += 2;
+      }
     }
+
     // Also do the same for the builtin compiler types Any and AnyObject, but
     // bump the impact even higher as they cannot conform to protocols at all.
     if (resolvedTy->isAny() || resolvedTy->isAnyObject())