Make crate module extension os and arch dependent (#2939)

This PR is follow up to #2453 and marks the `crate` extension as
`os_dependent` and `arch_dependent`.

For `crate.from_cargo`, the extension specifies reproducibility via the
`reproducible` attribute of `extension_metadata` which makes Bazel skip
the extension when writing the lockfile.

But in the case of `crate.from_specs`, the current implementation marks
the extension as non reproducible since the crates will not be backed by
a lockfile.
And because the `crate` module extension depends on `rust_host_tools`
(which are os / arch dependent), the entry in the lockfile for the
module extension includes the checksum of the `rustc` and `cargo`
binaries for whatever host it was resolved for.

This makes the bazel lock file platform dependent in that case.

This PR will result in a new os/arch specific entry in the lockfile for
users of `crate.from_specs`.
And will have no impact for users of `crate.from_cargo`.

Thanks to @fmeum for the guidance.