2.x: fix images of firstElement, flattenAsX, flatMapIterable

[akarnokd]

This PR links in the new images from #5130 for previously misleading marble diagrams of the operators.

[codecov]

Codecov Report

Merging #5208 into 2.x will decrease coverage by 0.01%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##               2.x    #5208      +/-   ##
===========================================
- Coverage     95.9%   95.88%   -0.02%     
+ Complexity    5678     5672       -6     
===========================================
  Files          621      621              
  Lines        40611    40611              
  Branches      5632     5632              
===========================================
- Hits         38947    38941       -6     
+ Misses         673      671       -2     
- Partials       991      999       +8

Impacted Files	Coverage Δ	Complexity Δ
src/main/java/io/reactivex/Maybe.java	100% <ø> (ø)	168 <0> (ø)	⬇️
src/main/java/io/reactivex/Single.java	99.32% <ø> (ø)	131 <0> (ø)	⬇️
...ain/java/io/reactivex/subjects/UnicastSubject.java	99.28% <ø> (+2.15%)	53 <0> (+2)	⬆️
src/main/java/io/reactivex/Flowable.java	100% <ø> (ø)	522 <0> (ø)	⬇️
...java/io/reactivex/processors/UnicastProcessor.java	96.81% <ø> (ø)	57 <0> (ø)	⬇️
src/main/java/io/reactivex/Observable.java	100% <ø> (ø)	506 <0> (ø)	⬇️
...reactivex/internal/operators/maybe/MaybeUsing.java	93.93% <0%> (-6.07%)	4% <0%> (ø)
...ternal/operators/observable/ObservablePublish.java	92.1% <0%> (-4.39%)	10% <0%> (-1%)
...reactivex/internal/operators/single/SingleAmb.java	96.36% <0%> (-3.64%)	9% <0%> (-1%)
...al/operators/observable/ObservableSampleTimed.java	93.33% <0%> (-3.34%)	3% <0%> (ø)
... and 34 more

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[akarnokd]

Plus UnicastX:

[vanniktech]

Those height & width resizes are due to the new images, right?

[akarnokd]

Yes, the default with is set to 640 and these new images are slightly bigger in their native form.

[JakeWharton]

👍

[akarnokd]

Thanks for the reviews guys!