[WIP] Bump the requirements to PHP 8.1

[mbabker]

According to the Packagist stats there was a large fall off PHP 7 users after the 3.14 release, which is when the requirement was bumped up to PHP 7.4. Since then, PHP 7.4 and 8.0 combined have had pretty small numbers on newer release branches and is generally now under 5% of the install base. So this PR bumps the requirement to PHP 8.1.

The overwhelming majority of the code changes are from adjusting the Rector and PHP-CS-Fixer configs to apply PHP 8.1 rulesets, with a second pass specifically on the tests to add type declarations there, then only minor corrections or tweaks by my own review along the way.

[codecov]

Codecov Report

❌ Patch coverage is 89.84772% with 20 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.38%. Comparing base (eb53dfc) to head (f0a5ec2).
⚠️ Report is 16 commits behind head on main.

Files with missing lines	Patch %	Lines
src/DoctrineExtensions.php	0.00%	4 Missing ⚠️
src/Translatable/TranslatableListener.php	78.57%	3 Missing ⚠️
src/Mapping/Event/Adapter/ORM.php	0.00%	2 Missing ⚠️
src/References/Mapping/Event/Adapter/ORM.php	50.00%	2 Missing ⚠️
src/Uploadable/Event/UploadableBaseEventArgs.php	0.00%	2 Missing ⚠️
src/Loggable/LoggableListener.php	66.66%	1 Missing ⚠️
src/Sluggable/Mapping/Event/Adapter/ODM.php	66.66%	1 Missing ⚠️
src/Tool/ClassUtils.php	0.00%	1 Missing ⚠️
src/Translator/TranslationProxy.php	66.66%	1 Missing ⚠️
...rc/Tree/Entity/Repository/NestedTreeRepository.php	75.00%	1 Missing ⚠️
... and 2 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2935      +/-   ##
==========================================
- Coverage   78.56%   78.38%   -0.18%     
==========================================
  Files         169      168       -1     
  Lines        8803     8702     -101     
==========================================
- Hits         6916     6821      -95     
+ Misses       1887     1881       -6     

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[mbabker]

Just for reference, all the changes to the minimum versions are either to get to a functional set of dependencies on PHP 8.1 (the transliterator package has errors on older versions, doctrine/common doesn't support some PHP 8.1 reflection changes until 3.1) or change to match the versions currently being installed on the prefer-lowest build. Considering how old some of these releases are it shouldn't be a big deal, I hope.