[languageserver] Ensure order of events

[svenefftinge]

It is critical that the order of read and write messages/notifications is kept when invoking the language server. Currently if the client sends a read and write request to the agent the order might be changed and as a consequence the read operation would be executed on the wrong state.

I think to preserve that we need to communicate document version ids with every REST call.

See also : microsoft/language-server-protocol#12

[TylerJewell]

Covered by the LSP epic.

[gorkem]

@svenefftinge is this something built into LSP4J now?