Problem: The codelens LSP module was using its own raw buffer events and
its own debounce mechanism for refreshing code lens in attached buffers.
Solution: Switch the module to using the LspNotify autocmd events.
LspNotify fires just after document versions are synced with the server
and provides a built in debounce mechanism for changes.
Additionally, this fixes some bugs with the previous implementation:
1. The workspace/codeLens/refresh handler re-requested codelens for all
buffers but when the response came back, it forced an extra redraw
after clearing the work the handler had just done.
2. Document synchronization was reworked to be more resilient to
multiple clients providing codelens for a single buffer. The latest
document version is now separately tracked per client (and per
client's lenses per row) instead of for the buffer as a whole. This
allows the on_win() function to properly redraw all codelens even
when different clients' responses for a particular document version
come back at different times.
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