WIP: Release native bazel_tools binaries separately

[fmeum]

This allows binaries such as the Windows test wrapper to be downloaded on non-Windows hosts, thus paving the way for cross platform builds using these tools.

Work towards #19587

TODO:

• Add publishing script
• Add def_parser (?)

[fmeum]

FYI @UebelAndre

[github-actions]

Thank you for contributing to the Bazel repository! This pull request has been marked as stale since it has not had any activity in the last 30 days. It will be closed in the next 30 days unless any other activity occurs. If you think this PR is still relevant and should stay open, please post any comment here and the PR will no longer be marked as stale.

[UebelAndre]

I don't have a windows machine to test with right now but isn't this solved for in some other way? I forget what the status of #19587 is currently.

[fmeum]

Linux builds of Bazel lack tw.exe, so this isn't fully solved yet. I am working on setting up toolchains_llvm_bootstrapped to build Bazel itself. At that point we can also add integration tests for host/exec/target all different.