Add support for textDocument/documentHighlight request

[rapgenic]

Hi, thank you all for the great project, which has helped me a lot while writing VHDL code!

In most of the other language servers, I use a lot the documentHighlight feature, which highlights all the occurrences of a symbol in the current file. Noticing that it was missing from this LS I attempted my own implementation

See the result here:

Video.del.2024-06-04.00-08-52.mp4

Edit

It seems that VScode has some kind of fallback that performs the same result even if the server does not have this capability! (I am actually using another editor - Zed - that would not do the same)

See the before and after in Zed:

Before

Video.del.2024-06-04.00-20-05.mp4

After

Video.del.2024-06-04.00-19-45.mp4

[Schottkyc137]

Thanks a lot for contributing!
This looks good to me so far. I have only added one comment which you can either ignore or implement; the choice is up to you.
If you want to ignore it, just mark the conversation as resolved and I will merge your changes.

[rapgenic]

What about something like this? I have tried it and it seems to perform actually faster!

[Schottkyc137]

What about something like this? I have tried it and it seems to perform actually faster!

Very nice, that's exactly what I had in mind.