[Python] Return every group from Regex.all_matches

[raams95]

Fixes #40562

Regex.all_matches built each output from range(m.lastindex + 1). lastindex is the index of the last group that matched, and with nested groups it is the outer group that closed last. It is None when the regex has no groups. Because of this:

p | beam.Create(['ab']) | beam.Regex.all_matches(r'((a)(b))')   # ['ab', 'ab'], groups 2 and 3 dropped
p | beam.Create(['a']) | beam.Regex.all_matches(r'(a)(b)?')     # ['a', 'a'], group 2 dropped
p | beam.Create(['aaa']) | beam.Regex.all_matches(r'a+')        # TypeError: unsupported operand type(s) for +: 'NoneType' and 'int'

Each output is now [m.group(), *m.groups()]: the entire match, then one entry per group of the regex, with None for a group that did not take part in the match. This is what Java's Regex.AllMatches returns (it adds null for such groups), and it is the same change #40399 made for Regex.find_all(..., Regex.ALL). Output for a regex whose groups all match, like the existing tests and the regex_all_matches snippet, does not change.

With this change the pipelines above print ['ab', 'ab', 'a', 'b'], ['a', 'a', None] and ['aaa'].

I added test_all_matched_returns_every_group to util_test.py. It runs the three cases in a TestPipeline. It fails with the TypeError before the change and passes after it. I also updated the docstring to describe the output.

Testing:

• pytest apache_beam/transforms/util_test.py (157 passed, 3 skipped)
• pytest apache_beam/examples/snippets/transforms/elementwise/ -k regex
• yapf --diff and ruff check on the changed files

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[github-actions]

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[tvalentyn]

thanks!

[tvalentyn]

I can merge once test suites finish, please ping if i don't get back to it in a day.

[tvalentyn]

(don't worry if there are unrelated failures in the CI)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.93%. Comparing base (76f6e6d) to head (abd778f).
⚠️ Report is 177 commits behind head on master.

Additional details and impacted files

@@              Coverage Diff              @@
##             master   #40563       +/-   ##
=============================================
+ Coverage     56.16%   79.93%   +23.76%     
=============================================
  Files          1124      488      -636     
  Lines        178336    82347    -95989     
  Branches       1489        0     -1489     
=============================================
- Hits         100170    65826    -34344     
+ Misses        75645    16521    -59124     
+ Partials       2521        0     -2521     

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