Support includeDeclaration in references request.

[mhanberg]

We should support this field in the references request so the client can decide if the definition should be included in the results.

Yeah, just pointing it out as it is the default client behaviour in those two clients.

I've checked the spec and it looks like there is already a context param that can be passed to references to specify if the declaration of the symbol itself should be returned.

Originally posted by @ogomezba in #131 (comment)