JSpecify: properly handle lambdas in anonymous inner classes

[msridhar]

Fixes #1156

When checking correctness of lambda overrides we get the type from javac's inferred type rather than using the enclosing class. Also, when getting the type of an anonymous class we add some extra assertions to ensure we find the right NewClassTree representing the anonymous class. I think we'll always get the right tree now, but the asserts give peace of mind.

[codecov]

Codecov Report

Attention: Patch coverage is 77.77778% with 2 lines in your changes missing coverage. Please review.

Project coverage is 88.17%. Comparing base (8786e88) to head (ec227a4).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
...ava/com/uber/nullaway/generics/GenericsChecks.java	66.66%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #1165   +/-   ##
=========================================
  Coverage     88.17%   88.17%           
- Complexity     2303     2305    +2     
=========================================
  Files            88       88           
  Lines          7533     7536    +3     
  Branches       1505     1506    +1     
=========================================
+ Hits           6642     6645    +3     
  Misses          448      448           
  Partials        443      443           

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