Sema: Two small cleanups for inout capture @NoEscape change

1) ValueDecl::hasInterfaceType() is broken because it means "we have
   computed the interface type" not "there is an interface type
   that can be computed". The distinction comes into play with decls
   where the interface type is never set explicitly.

2) Use foo->is<InOutType>() instead of isa<InOutType>(foo.getPointer());
   this is cleaner.

3) Use DeclContext::isLocalContext() instead of checking if the context
   is an AbstractFunctionDecl.

These should be NFC for the most part.

Author: slavapestov

lib/Sema/TypeCheckExpr.cpp

@@ -973,13 +973,10 @@ namespace {
       if (!validateForwardCapture(DRE->getDecl()))
         return { false, DRE };
 
-      bool isInOut = D->hasInterfaceType()
-                     && isa<InOutType>(D->getInterfaceType().getPointer());
+      bool isInOut = D->hasType() && D->getInterfaceType()->is<InOutType>();
       bool isNested = false;
-      if (auto f = AFR.getAbstractFunctionDecl()) {
-           isNested = f->getDeclContext()->getContextKind() ==
-        DeclContextKind::AbstractFunctionDecl;
-      }
+      if (auto f = AFR.getAbstractFunctionDecl())
+        isNested = f->getDeclContext()->isLocalContext();
 
       if (isInOut && !AFR.isKnownNoEscape() && !isNested) {
         if (D->getNameStr() == "self") {