Add TypeMap debug info.

[dereuromark]

Do people find this backed info useful?

/admin/setup/backend/type-map

I so far did. Helped me to find out which classes are currently mapped, and what types/classes are available.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 64.38356% with 26 lines in your changes are missing coverage. Please review.

Project coverage is 32.30%. Comparing base (c59c1f4) to head (bcc4e3e).

Files	Patch %	Lines
src/Utility/OrmTypes.php	60.52%	15 Missing ⚠️
src/Utility/ClassFinder.php	64.28%	10 Missing ⚠️
src/Controller/Admin/BackendController.php	85.71%	1 Missing ⚠️

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Additional details and impacted files

@@             Coverage Diff              @@
##             master      #36      +/-   ##
============================================
+ Coverage     31.09%   32.30%   +1.20%     
- Complexity      542      568      +26     
============================================
  Files            36       38       +2     
  Lines          1775     1848      +73     
============================================
+ Hits            552      597      +45     
- Misses         1223     1251      +28     

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