Track access paths of the form `Foo.this.bar`

[msridhar]

Fixes #936

We add limited tracking of such access paths, to handle null checks on fields from an enclosing class of a nested class.

[msridhar]

/benchmark

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 85.71429% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 87.04%. Comparing base (3bde26c) to head (3c8ff10).

Files	Patch %	Lines
...in/java/com/uber/nullaway/dataflow/AccessPath.java	85.71%	0 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #937 +/- ## ============================================ - Coverage 87.04% 87.04% -0.01% - Complexity 1993 1995 +2 ============================================ Files 77 77 Lines 6440 6447 +7 Branches 1249 1252 +3 ============================================ + Hits 5606 5612 +6 Misses 422 422 - Partials 412 413 +1 ```

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[github-actions[bot]]

Main Branch:

Benchmark                          Mode  Cnt   Score   Error  Units
AutodisposeBenchmark.compile      thrpt   25   9.212 ± 0.074  ops/s
CaffeineBenchmark.compile         thrpt   25   2.122 ± 0.023  ops/s
DFlowMicroBenchmark.compile       thrpt   25  25.144 ± 0.348  ops/s
NullawayReleaseBenchmark.compile  thrpt   25   1.283 ± 0.020  ops/s

With This PR:

Benchmark                          Mode  Cnt   Score   Error  Units
AutodisposeBenchmark.compile      thrpt   25   9.264 ± 0.093  ops/s
CaffeineBenchmark.compile         thrpt   25   2.120 ± 0.025  ops/s
DFlowMicroBenchmark.compile       thrpt   25  24.611 ± 0.319  ops/s
NullawayReleaseBenchmark.compile  thrpt   25   1.271 ± 0.018  ops/s