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.
The `.cargo/config.toml` override based workaround wasn't really
working, as while `cargo build|check` was reading that, `cargo metadata`
wasn't, ending up in a completely broken IDE experience.
For the moment, we just use a unified workspace `Cargo.toml` for all
extractors using the shared tree-sitter code, which has the downside of
making bazel pull in dependencies for all of them, and not being able to
do sparse checkouts for them. We should investigate and rivist this in
the future.
