support "workspace/willRenameFiles" request

[dannypsnl]

This will help the language server be able to send back to update edits when a file gets renamed.

Suppose we have a.rkt, c.rkt where c requires a, now we rename a.rkt to b.rkt. A language server supports this will return things like

(list (replace "c.rkt" (position ...) #:with-text "b.rkt")
      (replace ...) ; if more place requires `a.rkt`
      ...)

[Eugleo]

Is this something I can do only in Magic Racket, or do we need something implemented in the language server, first? If the latter, please close this issue here and open a similar one on the langserver repo.

[dannypsnl]

I think needs implement from server first