This is a hack to get around an issue on Apple devices caused by the
PosixEventEngine's `poll` poller not supporting fork. This PR disables
the EventEngine poller entirely in Python builds. It will therefore
prevent the release of the EventEngine generally, and prevent any
testing of EventEngine integration with gRPC Python, until the `poll`
poller is fixed.

This is a hack to get around an issue on Apple devices caused by the
PosixEventEngine's `poll` poller not supporting fork. This PR disables
the EventEngine poller entirely in Python builds. It will therefore
prevent the release of the EventEngine generally, and prevent any
testing of EventEngine integration with gRPC Python, until the `poll`
poller is fixed.

…3320)

This is a hack to get around an issue on Apple devices caused by the
PosixEventEngine's `poll` poller not supporting fork. This PR disables
the EventEngine poller entirely in Python builds. It will therefore
prevent the release of the EventEngine generally, and prevent any
testing of EventEngine integration with gRPC Python, until the `poll`
poller is fixed.




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Co-authored-by: AJ Heller <hork@google.com>

This is a hack to get around an issue on Apple devices caused by the
PosixEventEngine's `poll` poller not supporting fork. This PR disables
the EventEngine poller entirely in Python builds. It will therefore
prevent the release of the EventEngine generally, and prevent any
testing of EventEngine integration with gRPC Python, until the `poll`
poller is fixed.

…INSTANTIATE_POSIX_POLLER build define in Bazel tests (#39346)

The root cause of the ping timeout issue in Python that was recently
reported by Dataflow as well as in issue #38282 was because Python has
explicitly disabled the use of EventEngine polling using the
`GRPC_DO_NOT_INSTANTIATE_POSIX_POLLER` build flag (Reference:
#33279).

However, it was found that the issue could not be reproduced when
running via Bazel. This was because the
`GRPC_DO_NOT_INSTANTIATE_POSIX_POLLER` flag was not getting propagated
upstream to the Core layer, unless specifically defined as a compiler
option in `tools/bazel.rc` or passed via command-line.

Without this option, all the while the Python Bazel tests have been
testing something different than those covered by the setup.py build.

This PR hence does the following to fix the inconsistency:
- Update `tools/bazel.rc` with a python specific compiler option that is
included only when the specific `--config` command-line flag is included
when running via Bazel
 - Updates Python Bazel tests to include the new config flag