Annotate fewer extracted constants with types

Expose `isContextSensitive` from the checker and omit type annotations
for expressions for which it returns false.

src/compiler/checker.ts

@@ -171,6 +171,7 @@ namespace ts {
                 node = getParseTreeNode(node, isExpression);
                 return node ? getContextualType(node) : undefined;
             },
+            isContextSensitive,
             getFullyQualifiedName,
             getResolvedSignature: (node, candidatesOutArray, theArgumentCount) => {
                 node = getParseTreeNode(node, isCallLikeExpression);

src/compiler/types.ts

@@ -2739,6 +2739,8 @@ namespace ts {
         getAugmentedPropertiesOfType(type: Type): Symbol[];
         getRootSymbols(symbol: Symbol): Symbol[];
         getContextualType(node: Expression): Type | undefined;
+        /* @internal */ isContextSensitive(node: Expression | MethodDeclaration | ObjectLiteralElementLike | JsxAttributeLike): boolean;
+
         /**
          * returns unknownSignature in the case of an error.
          * @param argumentCount Apparent number of arguments, passed in case of a possibly incomplete call. This should come from an ArgumentListInfo. See `signatureHelp.ts`.