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.