Add progress or busy indication when extension is formatting.

Based on input from @Bobronium

This is definitely possible with the Progress APIs for LSP.
We just need to set `workDoneProgress: True` as the option when we register the Formatting feature `@LSP_SERVER.feature`
https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#documentFormattingOptions

Then in the params handle the progress token and respond accordingly to those params.
https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#clientInitiatedProgress

Start by locating the formatting feature registered with @LSP_SERVER.feature and the handler that receives formatting parameters. Read the linked LSP document-formatting and client-initiated-progress specifications, then trace how the progress token is handled. Done means the client shows a busy or progress indication while formatting is running.

Written by the indexing model from the issue text.