3.x: Add Single/Completable retryUntil + marbles

[akarnokd]

retryUntil was missing from Single and Completable.

Added marble for Maybe as well.

Related #6852, #5806

[codecov]

Codecov Report

Merging #6869 into 3.x will increase coverage by 0.04%.
The diff coverage is 100%.

@@ Coverage Diff @@ ## 3.x #6869 +/- ## ============================================ + Coverage 98.25% 98.29% +0.04%  - Complexity 6430 6433 +3  ============================================ Files 719 719 Lines 46746 46750 +4 Branches 6401 6401 ============================================ + Hits 45929 45953 +24  + Misses 293 283 -10  + Partials 524 514 -10

Impacted Files	Coverage Δ	Complexity Δ
src/main/java/io/reactivex/rxjava3/core/Maybe.java	100% <ø> (ø)	185 <0> (ø)	⬇️
...in/java/io/reactivex/rxjava3/core/Completable.java	100% <100%> (ø)	126 <1> (+1)	⬆️
...rc/main/java/io/reactivex/rxjava3/core/Single.java	100% <100%> (ø)	158 <1> (+1)	⬆️
...eactivex/rxjava3/processors/BehaviorProcessor.java	96.55% <0%> (-2.47%)	50% <0%> (ø)
...rnal/operators/observable/ObservableSwitchMap.java	91.57% <0%> (-2.11%)	3% <0%> (ø)
...ternal/operators/observable/ObservablePublish.java	97.29% <0%> (-1.81%)	16% <0%> (-1%)
...ternal/operators/flowable/FlowableSubscribeOn.java	96.61% <0%> (-1.7%)	2% <0%> (ø)
...internal/operators/flowable/FlowableSwitchMap.java	94.39% <0%> (-1.41%)	3% <0%> (ø)
...ernal/operators/flowable/FlowableFromIterable.java	95.18% <0%> (-1.07%)	5% <0%> (ø)
...ernal/operators/flowable/FlowableFlatMapMaybe.java	95.31% <0%> (-1.05%)	2% <0%> (ø)
... and 13 more

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