2.x: fix window() with time+size emission problems

[akarnokd]

The window() operator overload with time and size bound didn't work correctly when some windows were terminated by the timeout and others by the size. This PR fixes:

• the case when the operator restarts the time windows when the size bound is reached,
• leaking of the worker,
• the item counter not reset to zero when the time bound is reached,
• periodic window bound stopped working after the first window.

Related #5104 (again).

[codecov]

Codecov Report

Merging #5213 into 2.x will increase coverage by 0.09%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##                2.x    #5213      +/-   ##
============================================
+ Coverage     96.02%   96.12%   +0.09%     
- Complexity     5680     5690      +10     
============================================
  Files           621      621              
  Lines         40611    40617       +6     
  Branches       5632     5636       +4     
============================================
+ Hits          38998    39042      +44     
+ Misses          643      623      -20     
+ Partials        970      952      -18

Impacted Files	Coverage Δ	Complexity Δ
...ternal/operators/flowable/FlowableWindowTimed.java	84.68% <100%> (+1.01%)	4 <0> (ø)	⬇️
...al/operators/observable/ObservableWindowTimed.java	90.71% <100%> (+2.28%)	4 <0> (ø)	⬇️
.../operators/completable/CompletableConcatArray.java	93.75% <0%> (-6.25%)	2% <0%> (ø)
...internal/operators/completable/CompletableAmb.java	94.91% <0%> (-5.09%)	10% <0%> (-1%)
...ternal/operators/completable/CompletableUsing.java	95.23% <0%> (-4.77%)	4% <0%> (ø)
...reactivex/internal/operators/single/SingleAmb.java	96.36% <0%> (-3.64%)	9% <0%> (-1%)
...vex/internal/operators/single/SingleTakeUntil.java	91.8% <0%> (-3.28%)	2% <0%> (ø)
...x/internal/operators/flowable/FlowablePublish.java	93.83% <0%> (-1.77%)	9% <0%> (-1%)
...ternal/operators/observable/ObservablePublish.java	94.73% <0%> (-1.76%)	9% <0%> (-2%)
...al/operators/observable/ObservableSampleTimed.java	96.66% <0%> (-1.67%)	3% <0%> (ø)
... and 39 more

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