Recognize simple current-class objects for unused private method

[kylekatarnls]

Type: bugfix
Issue: Resolves #252 / Resolves #558 / Resolves #937
Breaking change: no

Recognize simple constructions of the current class for unused private method rule, such as:

• parameter typed (with strong type) as an instance of the current class (by name, FQCN, self or static)
• parameter that can be an instance of current class (nullable/union/intersection type that includes the current class)
• new Foo (with Foo matching FQCN of the current class, including self, static)
• clone $this (or clone of a variable recognized as of type of the current class)
• reference to variable that itself matches one of the rule above (recursively)

[codecov]

Codecov Report

❌ Patch coverage is 72.26891% with 33 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.85%. Comparing base (c14dcb9) to head (8354e05).
⚠️ Report is 40 commits behind head on master.

Files with missing lines	Patch %	Lines
src/main/php/PHPMD/Utility/CallableArray.php	0.00%	20 Missing ⚠️
src/main/php/PHPMD/Utility/LastVariableWriting.php	65.21%	8 Missing ⚠️
src/main/php/PHPMD/Rule/UnusedPrivateMethod.php	95.16%	3 Missing ⚠️
src/main/php/PHPMD/Utility/Seeker.php	85.71%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #1069      +/-   ##
============================================
- Coverage     92.56%   91.85%   -0.72%     
- Complexity     1252     1300      +48     
============================================
  Files           111      114       +3     
  Lines          3429     3534     +105     
============================================
+ Hits           3174     3246      +72     
- Misses          255      288      +33     

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