Fix multiple issues with NewClassTrees that have enclosing expressions

[msridhar]

Fixes #1188, exactly as suggested in that issue. This both simplifies the code and fixes a false negative with @Nullable enclosing expressions.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.22%. Comparing base (86febe1) to head (a2b4203).
Report is 1 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #1191      +/-   ##
============================================
+ Coverage     88.21%   88.22%   +0.01%     
+ Complexity     2314     2310       -4     
============================================
  Files            88       88              
  Lines          7553     7551       -2     
  Branches       1511     1508       -3     
============================================
- Hits           6663     6662       -1     
  Misses          446      446              
+ Partials        444      443       -1     

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[Copilot]

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

Comments suppressed due to low confidence (2)

nullaway/src/test/java/com/uber/nullaway/CoreTests.java:1138

• [nitpick] Consider renaming the test method 'issue1888' to a more descriptive name that reflects its intent, which could help with long-term code readability.

@Test public void issue1888() {

nullaway/src/main/java/com/uber/nullaway/NullAway.java:444

• [nitpick] The logic for handling the enclosing expression could be refactored into a helper method for improved clarity and maintainability.

ExpressionTree enclosingExpression = tree.getEnclosingExpression();