[Fix]: label-has-associated-control: ignore undetermined label text

[BillyLevin]

Attempt to fix #966

The rule no longer errors if the existence of label text cannot be determined. The criteria for not being able to determine whether the text exists are, for each child of the label:

1. It is a React component
2. It has no children
3. It is not registered as a control component. Unfortunately this means it would still error if the control component itself displays text, but I didn't see a way around that

I don't think this accounts for every case, but hopefully a good starting point

I followed the convention already used by making the new parameters for mayHaveAccessibleLabel optional, even though they're not. I assume that was to make it easier to write the unit tests. Happy to change that though if you'd like

[ljharb]

Seems good! I'll confirm the tests fail without the fix, and then merge.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.03%. Comparing base (a08fbcc) to head (a08fbcc).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1004   +/-   ##
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  Coverage   99.03%   99.03%           
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  Files         107      107           
  Lines        1660     1660           
  Branches      588      588           
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  Hits         1644     1644           
  Misses         16       16           

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