Version from extension descriptor should encoded into extension

[samansmink]

The version in the extension descriptor is now purely informational, it is not actually used. It is currently up to the extension developer to ensure the version of the extension that is built.

I'm considering removing the version field completely or forcing through ci that version and repo ref are identical

[rustyconover]

As long as the repo ref can be to a named tag it seems reasonable to me, but the only potential problem is if the tag is overridden after release.