2.x: Add Subject and Processor marbles

[akarnokd]

This PR adds the missing marble diagrams to the various Subject and Processor implementations:

AsyncSubject

PublishSubject

ReplaySubject

CompletableSubject

SingleSubject

MaybeSubject

AsyncProcessor

PublishProcessor

ReplayProcessor

[codecov]

Codecov Report

Merging #5816 into 2.x will increase coverage by 0.03%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##               2.x    #5816      +/-   ##
===========================================
+ Coverage     96.4%   96.44%   +0.03%     
- Complexity    5816     5817       +1     
===========================================
  Files          634      634              
  Lines        41761    41761              
  Branches      5796     5796              
===========================================
+ Hits         40259    40275      +16     
- Misses         574      575       +1     
+ Partials       928      911      -17

Impacted Files	Coverage Δ	Complexity Δ
...java/io/reactivex/processors/PublishProcessor.java	98.23% <ø> (ø)	43 <0> (ø)	⬇️
...n/java/io/reactivex/processors/AsyncProcessor.java	99.08% <ø> (ø)	52 <0> (ø)	⬇️
...main/java/io/reactivex/subjects/ReplaySubject.java	97.33% <ø> (ø)	49 <0> (ø)	⬇️
.../java/io/reactivex/processors/ReplayProcessor.java	99.35% <ø> (ø)	51 <0> (ø)	⬇️
...main/java/io/reactivex/subjects/SingleSubject.java	100% <ø> (ø)	38 <0> (ø)	⬇️
.../main/java/io/reactivex/subjects/MaybeSubject.java	100% <ø> (ø)	46 <0> (ø)	⬇️
...ain/java/io/reactivex/subjects/PublishSubject.java	97.8% <ø> (-2.2%)	38 <0> (-1)
.../main/java/io/reactivex/subjects/AsyncSubject.java	99.06% <ø> (ø)	52 <0> (ø)	⬇️
...java/io/reactivex/subjects/CompletableSubject.java	100% <ø> (ø)	36 <0> (ø)	⬇️
...internal/disposables/ArrayCompositeDisposable.java	96.42% <0%> (-3.58%)	15% <0%> (-1%)
... and 27 more

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