Swift: fix ARM build and add it to CI

[redsun82]

As pointed out in https://github.com/bazelbuild/bazel/issues/21768, bazel 7 moved multi-arch macOS toolchain support to apple_support, so building Swift (which must target x86_64 for now) was broken. Internally in the codeql CLI we were unaffected as we use a custom bundled toolchain.

This fixes building from this repository.

Moreover, various CI fixes have been added:

• added an ARM build to check this will keep on working for development on ARM machines
• removed the pretty much non-functioning shot at bazel cache, we will come back to it when we have a broader solution
• replaced sharing the extractor pack via cache with uploading and downloading it, using zstd compression