Support //tests/ios/unit-test/test-imports-app/... on Apple Silicon

[jerrymarino]

We moved the arm64 import_middleman into apple_library which misses when someone feeds an import into deps - consider how to handle that case.

Repro:

          bazelisk build --ios_multi_cpus=sim_arm64 --features apple.virtualize_frameworks  //tests/ios/unit-test/test-imports-app/...