Fix coder parsing for any non-standard composite coder types

[shunping]

fixes #32636

Inspired by #34348 (comment) and some offline discussions with @lostluck.

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[lostluck]

LGTM. Thanks!

[lostluck]

We need to also un-skip the packed coders test in Python with this PR. Basically delete the overload test_pack_combiners here: https://github.com/apache/beam/blob/master/sdks/python/apache_beam/runners/portability/prism_runner_test.py#L220

[shunping]

We need to also un-skip the packed coders test in Python with this PR. Basically delete the overload test_pack_combiners here: https://github.com/apache/beam/blob/master/sdks/python/apache_beam/runners/portability/prism_runner_test.py#L220

Done.

[lostluck]

Confirmed that test_pack_combiners runs and succeeds! The current failure seems like an unrelated flake, but we should re-run that to be sure, before merging in.