2.x: Improve the wording of the share() JavaDocs

[akarnokd]

This PR improves the wording of the Flowable.share() and Observable.share() operators and fixes a JavaDoc link display mistake:

[codecov]

Codecov Report

Merging #5824 into 2.x will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##                2.x    #5824   +/-   ##
=========================================
  Coverage     96.38%   96.38%           
+ Complexity     5816     5811    -5     
=========================================
  Files           634      634           
  Lines         41761    41761           
  Branches       5796     5796           
=========================================
  Hits          40253    40253           
+ Misses          583      579    -4     
- Partials        925      929    +4

Impacted Files	Coverage Δ	Complexity Δ
src/main/java/io/reactivex/Observable.java	100% <ø> (ø)	509 <0> (ø)	⬇️
src/main/java/io/reactivex/Flowable.java	100% <ø> (ø)	526 <0> (ø)	⬇️
.../operators/observable/ObservableFlatMapSingle.java	88.8% <0%> (-5.98%)	2% <0%> (ø)
.../io/reactivex/internal/functions/ObjectHelper.java	94.73% <0%> (-5.27%)	20% <0%> (-1%)
...ava/io/reactivex/processors/BehaviorProcessor.java	91.03% <0%> (-4.04%)	60% <0%> (+1%)
...nternal/operators/parallel/ParallelReduceFull.java	91.17% <0%> (-3.93%)	2% <0%> (ø)
...tivex/internal/schedulers/TrampolineScheduler.java	92.3% <0%> (-2.57%)	6% <0%> (ø)
...activex/internal/observers/QueueDrainObserver.java	61.53% <0%> (-2.57%)	12% <0%> (-1%)
...va/io/reactivex/internal/queue/SpscArrayQueue.java	97.61% <0%> (-2.39%)	22% <0%> (-1%)
...nternal/operators/parallel/ParallelSortedJoin.java	92.75% <0%> (-2.18%)	2% <0%> (ø)
... and 29 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 173156d...3b8db09. Read the comment docs.

[artem-zinnatullin]

small typo

[artem-zinnatullin]

"abd" -> "and"