Migrate gRPC ObjC PerfTest, TvTests and MacTests to bazel

[dennycd]

Cocoapod Targets

• PerfTests
• TvTests
• MacTests

Also we should enable GRPC_VERBOSITY=debug environment variable when running these tests

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cc @jtattermusch

[jtattermusch]

The targets //src/objective-c/tests:TvTests and //src/objective-c/tests:MacTests already exist, but their build seems broken.

PerfTests bazel target doesn't exist at all.

[jtattermusch]

Once the targets work reliably, they can be added to the kokoro job being created here: grpc/grpc#29599

[jtattermusch]

More accurate state of affairs (and what remains to be done) is being added as a list of TODOs here: https://github.com/grpc/grpc/pull/29665/files#diff-26e0bc5bba55be18a1e28b707c1768be5c3de415944115ec3b4eb006b1d39693

[jtattermusch]

• The MacTests are already running continuously:
  https://github.com/grpc/grpc/blob/741738695605fb394c1dd86674d3da055c728d00/tools/internal_ci/macos/grpc_objc_bazel_test.sh#L52

• The TvTests are still disabled in the bazel job:
  https://github.com/grpc/grpc/blob/741738695605fb394c1dd86674d3da055c728d00/tools/internal_ci/macos/grpc_objc_bazel_test.sh#L49

• PerfTests actually aren't being run by run_tests.py (looks like it's manual-only test that never runs on CI)? If that's true, I don't think migrating them to bazel is required for this issue.

@HannahShiSFB can you try to enable the TvTests with bazel?