[Basic] hasFeature should succeed for promoted language features

Merge `$<Feature>` and `hasFeature` implementations.
  - `$<Feature>` did not support upcoming language features.
  - `hasFeature` did not support promoted language features and also
    didn't take into account `Options` in `Features.def`.

Remove `Options` entirely, it was always one of three cases:
  - `true`
  - `langOpts.hasFeature`
  - `hasSwiftSwiftParser`

Since `LangOptions::hasFeature` should always be used anyway, it's no
longer necessary. `hasSwiftSwiftParser` can be special cased when adding
the default promoted language features (by removing those features).

Resolves rdar://117917456.

lib/Frontend/ModuleInterfaceLoader.cpp

@@ -1624,8 +1624,8 @@ void InterfaceSubContextDelegateImpl::inheritOptionsForBuildingInterface(
   });
 
   if (LangOpts.hasFeature(Feature::LayoutPrespecialization)) {
-    genericSubInvocation.getLangOptions().Features.insert(
-      Feature::LayoutPrespecialization);
+    genericSubInvocation.getLangOptions().enableFeature(
+        Feature::LayoutPrespecialization);
   }
 
   // Validate Clang modules once per-build session flags must be consistent