GeezerVison

This essentially undoes #9746, which only contextually typed object
literal methods, but did so early, during `getSignatureFromDeclaration`.
The compiler now contextually types everything, as it did before, but
only looks for a contextual type if there is no declared `this` type.

After #9746, a member list request from the language service would call
`getSignatureFromDeclaration`, but it would never get a contextual this-type,
because contextual typing was only enabled for object literal methods.