2.x: fix replay().refCount() leaking items between connections

[akarnokd]

This PR updates Observable.replay() and Flowable.replay() for 2.x to not leak items between reconnections when run with .refCount(). The replay() operator is designed to hold onto the buffer even after its completion so late subscribers can still receive the cached data. Only a new connect() clears this data which may or may not happen. Since refCount ensures that there won't be any latecommers to an already completed connection (because it also drops its current subscribers on termination or when reaching zero), the replay() can be reset to an empty state.

Related: #5172, #5181.

[codecov]

Codecov Report

Merging #5182 into 2.x will decrease coverage by 0.03%.
The diff coverage is 100%.

@@             Coverage Diff             @@
##                2.x   #5182      +/-   ##
===========================================
- Coverage     96.04%     96%   -0.04%     
- Complexity     5655    5665      +10     
===========================================
  Files           621     621              
  Lines         40320   40336      +16     
  Branches       5610    5616       +6     
===========================================
+ Hits          38725   38726       +1     
- Misses          630     640      +10     
- Partials        965     970       +5

Impacted Files	Coverage Δ	Complexity Δ
.../internal/operators/flowable/FlowableRefCount.java	98.71% <100%> (+0.06%)	7 <0> (ø)	❌
...ernal/operators/observable/ObservableRefCount.java	98.68% <100%> (+0.07%)	7 <0> (ø)	❌
...nternal/operators/observable/ObservableReplay.java	97.77% <100%> (-0.26%)	22 <4> (+3)
...ex/internal/operators/flowable/FlowableReplay.java	90.69% <100%> (+0.07%)	21 <4> (+4)	✅
...al/operators/observable/ObservableSampleTimed.java	88.33% <0%> (-8.34%)	3% <0%> (ø)
...in/java/io/reactivex/subjects/BehaviorSubject.java	84.97% <0%> (-4.67%)	56% <0%> (+1%)
...a/io/reactivex/internal/util/QueueDrainHelper.java	60.28% <0%> (-4.26%)	32% <0%> (-3%)
...rnal/operators/completable/CompletableTimeout.java	94% <0%> (-4%)	2% <0%> (ø)
.../operators/observable/ObservableFlatMapSingle.java	92.53% <0%> (-3.74%)	2% <0%> (ø)
...reactivex/internal/operators/single/SingleAmb.java	96.36% <0%> (-3.64%)	9% <0%> (-1%)
... and 33 more

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