* cache all tokens from various range requests for a given document
version
- all new token highlights are merged with previous highlights to
maintain order and the "marked" property
- this allows the tokens to stop flickering once they've loaded once
per document version
* abandon the processing coroutine if the request_id has changed instead
of relying only on the document version
- this will improve efficiency if a new range request is made while a
previous one was processing its result
* apply new highlights from processing coroutine directly to the current
result when the version hasn't changed
- this allows new highlights to be immediately drawable once they've
processed instead of waiting for the whole response to be processed
at once
* rpc layer was changed to provide the request ID back in success
callbacks, which is then provided as a request_id field on the handler
context to lsp handlers
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