[BEAM-11936] Add configuration parameter for suppressing error-prone UnusedVariable check

[TheNeuralBit]

... and sets the parameter in every applyJavaNature usage.

This will enable breaking up the changes for this check into several smaller PRs.

ValidatesRunner compliance status (on master branch)

Lang	ULR	Dataflow	Flink	Samza	Spark	Twister2
Go	---					---
Java
Python	---					---
XLang						---

Examples testing status on various runners

Lang	ULR	Dataflow	Flink	Samza	Spark	Twister2
Go	---	---	---	---	---	---	---
Java	---		---	---	---	---	---
Python	---	---	---	---	---	---	---
XLang	---	---	---	---	---	---	---

Post-Commit SDK/Transform Integration Tests Status (on master branch)

Go	Java	Python

Pre-Commit Tests Status (on master branch)

---	Java	Python	Go	Website	Whitespace	Typescript
Non-portable
Portable	---			---	---	---

See .test-infra/jenkins/README for trigger phrase, status and link of all Jenkins jobs.

GitHub Actions Tests Status (on master branch)

See CI.md for more information about GitHub Actions CI.

[TheNeuralBit]

R: @kennknowles @benWize

[codecov]

Codecov Report

Merging #16010 (7ffc904) into master (9fe2a27) will decrease coverage by 0.00%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #16010      +/-   ##
==========================================
- Coverage   83.62%   83.62%   -0.01%     
==========================================
  Files         445      445              
  Lines       61382    61382              
==========================================
- Hits        51329    51328       -1     
- Misses      10053    10054       +1     

Impacted Files	Coverage Δ
sdks/python/apache_beam/utils/interactive_utils.py	87.80% <0.00%> (-2.44%)	⬇️
.../python/apache_beam/transforms/periodicsequence.py	96.72% <0.00%> (-1.64%)	⬇️
sdks/python/apache_beam/internal/metrics/metric.py	90.00% <0.00%> (-1.00%)	⬇️
...hon/apache_beam/runners/worker/bundle_processor.py	93.64% <0.00%> (+0.12%)	⬆️
...ks/python/apache_beam/runners/worker/sdk_worker.py	89.41% <0.00%> (+0.16%)	⬆️

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[TheNeuralBit]

Run Java_Examples_Dataflow PreCommit

[TheNeuralBit]

Run Java PreCommit

[TheNeuralBit]

Run Java_Examples_Dataflow PreCommit

[TheNeuralBit]

Run Java_Examples_Dataflow PreCommit