feat(grouping): Add helper to combine hints

[lobsterkatie]

When a frame is affected by both an in-app rule and a contributes rule, the split enhancements allow us to get both hints, rather than having one clobber the other (as is the case now). That does not mean, however, that both hints are always relevant. This PR adds a helper, _combine_hints, to appropriately use or ignore each hint, and combine them when necessary. It's not yet used, but will be when we switch to actually using the split enhancements, rather than just running them alongside the non-split ones.

Note that _combine_hints needs the final contributes value to already be in place when it runs, so this also moves the setting of that value earlier in assemble_stacktrace_component.

[codecov]

Codecov Report

Attention: Patch coverage is 90.47619% with 2 lines in your changes missing coverage. Please review.

⚠️ Parser warning

The parser emitted a warning. Please review your JUnit XML file:

Warning while parsing testcase attributes: Limit of string is 1000 chars, for name, we got 2083 at 1:156897 in /home/runner/work/sentry/sentry/.artifacts/pytest.junit.xml

Files with missing lines	Patch %	Lines
src/sentry/grouping/enhancer/__init__.py	87.50%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #91833      +/-   ##
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- Coverage   87.64%   87.64%   -0.01%     
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  Files       10350    10350              
  Lines      586586   586605      +19     
  Branches    22574    22574              
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+ Hits       514115   514129      +14     
- Misses      72026    72031       +5     
  Partials      445      445