Add highlights to the completions

[WeetHet]

Adds label_for_completion and label_for_symbol which allow Zed to highlight symbols when searching or when using auto completion

[WeetHet]

This deliberately does not bump up the version, as I wanna also set up automatic downloading of metals before bumping the version all the way up to 0.1.0

[WeetHet]

I am trying to fill in here as at least an ad-hoc maintainer, so forgive any questions that might not make sense.

Could you point to docs for those methods? I don't exactly see how they are related to your screenshot

There are probably no docs for these, and I'm navigating more based on the general sense of what is going on in the other extensions. As far as I know, for CodeLabel:

• code is the code passed to the tree-sitter for highlighting
• spans are the parts of the code displayed to the user when using auto completion or symbol search
• filter_range is a range over something? that is used to search the completions provided by the language server. It's certainly not a range over the code, so I presume it's the range over the displayed part

The kinds are very poorly documented everywhere, so I can't say much about those, I just looked at what metals returns and adapted to that