This PR introduces a bazel and `rules_rust`-based build system
for the ruby extractor and language pack.
This replacese the existing, `cargo` and `cross`-based build system.
For local development, nothing changes, and the existing `cargo`-based
build still keeps working as-is.
We no longer need to use `cross` to compile our Linux binaries,
as we now can link against our hermetic C++ toolchain, which ships
with an old enough glibc, so that we don't run into symbol version issues
when deploying the binaries to older systems.
Besides the one change in dependency (explained in detail in `Cargo.toml`
and in https://github.com/github/codeql/pull/15595), nothing ought to
change in how we build the extractor.
