Add rule for generating xctestrun bundles

I am looking to add support for creating xctestrun bundles from `ios_unit_test` and `ios_ui_test` bundles (originally attempted [here](https://github.com/bazelbuild/rules_apple/pull/1994)) . I noticed that recently there were significant changes to how bundling works for tests leading me to make a draft PR of my current attempt [here](https://github.com/bazelbuild/rules_apple/pull/2174).

1. Should we make a new rule to make xctestrun bundles or should running bazel build create these bundles when using the new xctestrunner
2. What is the correct starting point for starting this work given the significant changes?