Remove need to use JSpecify's @Nullable annotation

[msridhar]

Fixes #1139. There are real scenarios where projects may not want to ship with a JSpecify dependence; see #1139 (comment). So, we remove any cases where we were specifically checking for or using JSpecify's @Nullable annotation.

Most of the code changes are due to the fact that now, we check if an annotation is a @Nullable annotation using Nullness.hasNullableAnnotation, which requires a Config object as a parameter. So we need to thread a Config object as a parameter through a bunch of methods.

[codecov]

Codecov Report

Attention: Patch coverage is 93.10345% with 4 lines in your changes missing coverage. Please review.

Project coverage is 88.22%. Comparing base (f064222) to head (3ef0323).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
...ava/com/uber/nullaway/generics/GenericsChecks.java	93.33%	0 Missing and 3 partials ⚠️
...laway/generics/PreservedAnnotationTreeVisitor.java	85.71%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #1142      +/-   ##
============================================
- Coverage     88.24%   88.22%   -0.02%     
+ Complexity     2263     2260       -3     
============================================
  Files            85       85              
  Lines          7314     7312       -2     
  Branches       1458     1461       +3     
============================================
- Hits           6454     6451       -3     
  Misses          432      432              
- Partials        428      429       +1     

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[akshayutture]

Why do we no longer need 'state' (VisitorState) here (and in other places in this diff)?

[msridhar]

It's because hasNullableAnnotation (https://github.com/uber/NullAway/pull/1142/files#diff-82d66c6ba15b87acc24509d7a3440bbe7606944197b929733d315fbe0a025435L1159-L1171) used to rely on the state object in order to check for the presence of the JSpecify @Nullable annotation. Now we don't do that, so in various places state is no longer needed (but config is).