This update changes the extension's publisher from "matklad" to
"rust-lang" and moves it to `vscode-extensions.rust-lang.rust-analyzer`,
but keeps `vscode-extensions.matklad.rust-analyzer` for backwards
compatibility. It also bumps the version number from 0.2.xxx to 0.3.xxx,
as described in changelog #129.5:
https://rust-analyzer.github.io/thisweek/2022/05/17/changelog-129-5.html
The release tag was out-of-date even though the extension was updated
regularly. Ideally, the update script might increment it on its own,
like the rust-analyzer update script already does.
