support "workspace/willRenameFiles" request

[dannypsnl]

In fact, the point is to let racket-langserver handle the workspace, with a defined scope server can do more like renaming for the workspace or finding all usages in the workspace.

reference

• Need to update ServerCapabilities
• https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#workspace_willRenameFiles