LSP: Add UI support for formatting
IdeLspFormatter is the interface to request textDocument/formatting to the Server, but while in VSCode a format document and format range is exposed to the user, Builder hasn't or at least is not obvious, how to initiate this request.
GVls 18.0 and with the #1365 (closed) and !320 (merged) formatting support will be added for Vala code, so could be useful to add a quick UI to access this feature.