LSP - Support inheritdoc

[sebasmonia]

The server should give the LSP client the inherited docs in this case.

Let me know if you think this is something the client should do, but it seems the server has the context to resolve from whom to pick up the documents.

Example:
ITheContract defines DoYourThing() with /// <summary> etc. etc. etc.
Then Concrete : ITheContract implements DoYourThing() and documents with /// <inheritdoc />