publish a source tarball with version and grammars

[the-mikedavis]

A few changes here:

• publish the source tarball with grammars already fetched and including a VERSION file with the tag name
• read the release VERSION file for the current version

for example:

$ cargo run -- --version
helix 22.03 (b222aba3)

Separating out the fetching and compression of grammars speeds up the workflow quite a bit. A lot of time would get wasted on upload/download-artifacts for the files from runtime/grammars/sources

[the-mikedavis]

I have this running on my fork, should finish up in the next 10min

woohoo, it works and the binary size isn't massive! https://github.com/the-mikedavis/helix/actions/runs/2055527816