Improve diagnostic when string from property is not assignable to string literal.

**TypeScript Version:** 3.1.0-dev.20180810 **Code** ```ts interface IceCreamOptions { readonly cherry: "yes" | "no" } declare function iceCream(options: IceCreamOptions): void; const options = { cherry: "yes" }; iceCream(options); ``` **Expected behavior:** Error message recommending to add a type annotation to `options`. This should be detectable because the source of the failing property is a `PropertyAssignment` in an object literal being assigned to a variable. (If there is no variable assignment, we could still recommend using ``"yes" as "yes"` although that isn't as pretty.) Could also come with a codefix. Note that in JS the fix is slightly different: put `/** @type {IceCreamOptions} */` before the `const` or use `/** @type {"yes"} */ ("yes")`. **Actual behavior:** Error messages says `Type 'string' is not assignable to type '"yes" | "no"'.` with no information on how to fix it.