codeintel: Reduce data returned from code intel ranges requests

Created by: efritz

This is a partial resolution to https://github.com/sourcegraph/sourcegraph/issues/13733.

This PR drastically reduces the amount of data that needs to be returned by removing any references to locations outside of the current document, which is all we currently care about. This is done in a bit of a naive way which doesn't save any backend time, but does reduce the time spent transferring data, parsing the JSON, converting the data in the extension. This should also reduce the memory footprint of the extension.