* The ungram file is now taken from the rust-analyzer dependencies
pulled in by bazel
* the grammar parsing code is not published, so it must be taken
directly from rust-analyzer code. That part should be less prone to be
updated than the ungram file, so it does not necessarily need to be
in sync with the rust-analyzer version is used elsewhere.
* both need some patches. The former is patched during build, the latter
during loading in `MODULE.bazel`.
We've been observing some performance issues using crate_universe on CI.
Therefore, we're moving to vendor the auto-generated BUILD files
in our repository. This should provide a nice speed boost, while
getting rid of the complexity of the "rust cache" job we've been using
when we had a lot of git dependencies.
This PR includes a vendor script, and I'll put up a CI job internally
that runs that vendor script on Cargo.toml and Cargo.lock changes, to check
that the vendored files are in sync.
