CodeCoverage: refactor to pure Singleton

[Slamdunk]

Hi, this PR sets a clear line between the Singleton instance and its behaviour for:

1. \PHPUnit\TextUI\Configuration\CodeCoverageFilterRegistry
2. \PHPUnit\Runner\CodeCoverage

Allowing to have local instances that do not interfere with active PHPUnit run.

For PHPUnit the benefit is that these classes become now unit-testable, if needed.
For external project like ParaTest (I'm aware that I'm dealing with @internal classes) this means these classes can be used without mangling PHPUnit internal state.

[codecov]

Codecov Report

Merging #5179 (6eceb69) into 10.0 (b4d036a) will decrease coverage by 0.02%.
The diff coverage is 25.98%.

❗ Current head 6eceb69 differs from pull request most recent head 69b138a. Consider uploading reports for the commit 69b138a to get more accurate results

@@             Coverage Diff              @@
##               10.0    #5179      +/-   ##
============================================
- Coverage     81.28%   81.27%   -0.02%     
- Complexity     5841     5843       +2     
============================================
  Files           629      629              
  Lines         18511    18512       +1     
============================================
- Hits          15047    15045       -2     
- Misses         3464     3467       +3     

Impacted Files	Coverage Δ
.../Command/Commands/WarmCodeCoverageCacheCommand.php	0.00% <0.00%> (ø)
src/Runner/CodeCoverage.php	11.51% <20.23%> (+1.89%)	⬆️
...extUI/Configuration/CodeCoverageFilterRegistry.php	21.21% <29.41%> (+10.86%)	⬆️
src/Runner/PhptTestCase.php	68.93% <44.44%> (ø)
src/Util/PHP/AbstractPhpProcess.php	79.33% <50.00%> (ø)
src/TextUI/Application.php	82.08% <60.00%> (ø)
src/Framework/TestRunner.php	86.99% <75.00%> (ø)
src/Event/Value/Test/TestCollection.php	40.00% <0.00%> (-20.00%)	⬇️
...stSuite/TestSuiteForTestMethodWithDataProvider.php	37.50% <0.00%> (-12.50%)	⬇️
src/Event/Value/TestSuite/TestSuite.php	96.22% <0.00%> (-3.78%)	⬇️
... and 5 more

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