Clean up the Test Double generator and runtime

[sebastianbergmann]

This closes #5246, #5247, #5248, #5249, #5250, #5310, #5311, #5312, #5313, #5314, #5316, #5321, #5416, #5424, and #5536 as well as deletes now unused code and simplifies existing code.

[codecov]

Codecov Report

Attention: Patch coverage is 90.55118% with 12 lines in your changes missing coverage. Please review.

Project coverage is 92.22%. Comparing base (778070d) to head (85cd717).

Files	Patch %	Lines
src/Framework/MockObject/Generator/MockBuilder.php	78.84%	11 Missing ⚠️
src/Framework/MockObject/Generator/Generator.php	97.50%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #5697      +/-   ##
============================================
- Coverage     92.34%   92.22%   -0.13%     
+ Complexity     6554     6436     -118     
============================================
  Files           699      687      -12     
  Lines         19772    19238     -534     
============================================
- Hits          18259    17742     -517     
+ Misses         1513     1496      -17     

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