3.x: remove test from testXXX method names, create a validator

[maksim-m]

Fix #6518.

• Create validator
• Automatically rename methods "testXXX" to "xxx" (analog to FixLicenseHeaders check)
• Rename methods

[codecov]

Codecov Report

Merging #6525 into 3.x will increase coverage by 0.03%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##                3.x    #6525      +/-   ##
============================================
+ Coverage     98.16%   98.19%   +0.03%     
+ Complexity     6251     6248       -3     
============================================
  Files           675      675              
  Lines         45011    45011              
  Branches       6211     6211              
============================================
+ Hits          44183    44199      +16     
+ Misses          286      280       -6     
+ Partials        542      532      -10

Impacted Files	Coverage Δ	Complexity Δ
...nternal/operators/observable/ObservableCreate.java	93.16% <0%> (-5.13%)	2% <0%> (ø)
...va/io/reactivex/internal/queue/SpscArrayQueue.java	97.61% <0%> (-2.39%)	22% <0%> (-1%)
...ernal/operators/flowable/FlowableFlatMapMaybe.java	92.75% <0%> (-1.94%)	2% <0%> (ø)
...a/io/reactivex/internal/util/QueueDrainHelper.java	98.61% <0%> (-1.39%)	57% <0%> (-1%)
.../operators/mixed/FlowableSwitchMapCompletable.java	98.94% <0%> (-1.06%)	2% <0%> (ø)
...l/operators/observable/ObservableTimeoutTimed.java	99.15% <0%> (-0.85%)	3% <0%> (ø)
.../operators/maybe/MaybeFlatMapIterableFlowable.java	97.54% <0%> (-0.82%)	2% <0%> (ø)
...reactivex/internal/queue/SpscLinkedArrayQueue.java	96.82% <0%> (-0.8%)	38% <0%> (-1%)
...ain/java/io/reactivex/subjects/UnicastSubject.java	99.36% <0%> (-0.64%)	64% <0%> (-1%)
...x/internal/operators/flowable/FlowableFlatMap.java	87.63% <0%> (-0.53%)	3% <0%> (ø)
... and 17 more

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[akarnokd]

I was doing a massive set of changes to the test files myself so it would be great you rolled back the renames, kept the validator code but not fail when violations are found. I'll merge in #6526, then just the validator, then we can enable the offline/CI failure mode and fix the names in a fresh PR.

[maksim-m]

I added @Ignore annotation for now and removed a commit with the actual renaming.
I will open a new PR when #6526 and this one are merged.