Fixes from RxJava since April 21

[akarnokd]

Applied changes:

• Pull 5449: Remove the @NonNull annotation from Function
• Pull 5447: Remove @NonNull annotation in Consumer method parameter
• Pull 5444: Fix wording in Async and Publish processors javadoc.
• Pull 5441: fix periodic scheduler purging config not honored
• Pull 5440: concat to report isDisposed consistently with termination
• Pull 5436: Gradle to use less memory, missed an export command
• Pull 5434: fix time bounded replaySubject getValue() inconsistency with getValues() on old items
• Pull 5432: fix/clarify the Observable class' javadoc
• Pull 5427: fix buffer(time, maxSize) duplicating buffers on time-size race
• Pull 5422: more eager cancellation in flatMapX
• Pull 5421: attempt to fix a few time-sensitive tests.
• Pull 5419: fix periodic scheduling with negative period causing IAE
• Pull 5415: fix doOnNext failure not triggering doOnError when fused
• Commit 84d333e0: Fix a small typo in Single.delay
• Commit 4d8f008c: add missing 'the' to the changed sentences of 5413
• Pull 5413: Add empty source clauses to javadocs of combineLatest operators
• Pull 5409: Corrected Single.delay documentation
• Pull 5406: Fix javadoc for Observable.reduce() and Observable.reduceWith()
• Pull 5407: DefaultSubscriber javadoc sample fix
• Pull 5405: DefaultObserver javadoc example fix
• Pull 5403: Fix documentation of Single.doAfterTerminate.
• Pull 5386: add subscribeOn overload to avoid same-pool deadlock with create
• Pull 5391: Changed minimum value of rx2.buffer-size to 1
• Pull 5379: add missing null checks on values returned by user functions
• Pull 5383: Fixed Javadoc for SingleFlatMapIterableObservable. (already fixed from an earlier commit)
• Pull 5378: make SingleMap not allow map function return null
• Pull 5367: make sure interval+trampoline can be stopped
• Commit 0b0355e3: Replace Action1 with Consumer in docs
• Pull 5354: Fix typo in error message.
• Pull 5351: update some marbles of Observable
• Pull 5347: Fix Javadoc of FunctionX
• Pull 5344: add tryOnError to create/XEmitter API
• Pull 5343: Fix Javadoc for Maybe.toSingle
• Pull 5324: Mark VolatileSizeArrayList as RandomAccess list
• Pull 5310: Apply promotions for v2.1
• Pull 5309: Fix Javadoc of Flowable.toObservable
• Pull 5307: Apply promotions for v2.1

[codecov]

Codecov Report

Merging #2 into master will increase coverage by 0.08%.
The diff coverage is 87.54%.

@@            Coverage Diff             @@
##           master       #2      +/-   ##
==========================================
+ Coverage   94.48%   94.57%   +0.08%     
==========================================
  Files         661      662       +1     
  Lines       42121    42279     +158     
  Branches     5818     5849      +31     
==========================================
+ Hits        39797    39984     +187     
+ Misses       1311     1290      -21     
+ Partials     1013     1005       -8

Impacted Files	Coverage Δ
.../reactivex/flowable/processors/AsyncProcessor.java	97.45% <ø> (ø)	⬆️
...lowable/internal/operators/FlowableReduceWith.java	93.18% <ø> (ø)	⬆️
.../common/exceptions/ProtocolViolationException.java	100% <ø> (ø)	⬆️
...ommon/internal/queues/AbstractMpscLinkedQueue.java	100% <ø> (ø)	⬆️
.../reactivex/observable/RxJavaObservablePlugins.java	89.28% <ø> (ø)	⬆️
...ivex/common/exceptions/UndeliverableException.java	100% <ø> (ø)	⬆️
...reactivex/observable/subjects/BehaviorSubject.java	91.66% <ø> (+6.77%)	⬆️
.../reactivex/observable/subjects/PublishSubject.java	97.87% <ø> (-2.13%)	⬇️
.../internal/operators/MaybeFlatMapSingleElement.java	100% <ø> (ø)	⬆️
...eactivex/observable/observers/DefaultObserver.java	100% <ø> (ø)	⬆️
... and 156 more

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