3.x: Improve Javadocs of Connectable sources

[akarnokd]

Improve the styling and wording of ConnectableObservable and ConnectableFlowable.

[codecov]

Codecov Report

Merging #7127 (886f791) into 3.x (7e7b223) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##                3.x    #7127      +/-   ##
============================================
- Coverage     99.54%   99.53%   -0.02%     
  Complexity     6674     6674              
============================================
  Files           742      742              
  Lines         47273    47273              
  Branches       6376     6376              
============================================
- Hits          47060    47052       -8     
- Misses           98      100       +2     
- Partials        115      121       +6     

Impacted Files	Coverage Δ	Complexity Δ
...activex/rxjava3/flowables/ConnectableFlowable.java	100.00% <ø> (ø)	12.00 <0.00> (ø)
...vex/rxjava3/observables/ConnectableObservable.java	100.00% <100.00%> (ø)	12.00 <4.00> (ø)
...l/operators/observable/ObservableFlatMapMaybe.java	91.54% <0.00%> (-7.05%)	2.00% <0.00%> (ø%)
...erators/completable/CompletableConcatIterable.java	95.91% <0.00%> (-4.09%)	2.00% <0.00%> (ø%)
...x/rxjava3/internal/operators/single/SingleAmb.java	96.61% <0.00%> (-3.39%)	9.00% <0.00%> (-1.00%)
...vex/rxjava3/internal/operators/maybe/MaybeAmb.java	96.96% <0.00%> (-3.04%)	10.00% <0.00%> (-1.00%)
...eactivex/rxjava3/processors/BehaviorProcessor.java	97.48% <0.00%> (-2.52%)	50.00% <0.00%> (ø%)
...nternal/operators/observable/ObservableWindow.java	98.21% <0.00%> (-1.79%)	3.00% <0.00%> (ø%)
.../operators/observable/ObservableFlatMapSingle.java	94.44% <0.00%> (-1.59%)	2.00% <0.00%> (ø%)
...ternal/operators/completable/CompletableMerge.java	97.29% <0.00%> (-1.36%)	2.00% <0.00%> (ø%)
... and 15 more

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