3.x: Make using() resource disposal order consistent with eager-mode

[akarnokd]

Make the resource disposal order in all using implementations are consistent with the eagerness of the operator:

eager: dispose resource then dispose the upstream
non-eager: dispose the upstream then dispose the resource.

Fixes: #6347

[codecov]

Codecov Report

Merging #6534 into 3.x will increase coverage by 0.03%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##                3.x    #6534      +/-   ##
============================================
+ Coverage     98.21%   98.24%   +0.03%     
- Complexity     6189     6190       +1     
============================================
  Files           680      680              
  Lines         44883    44905      +22     
  Branches       6193     6198       +5     
============================================
+ Hits          44081    44118      +37     
+ Misses          261      249      -12     
+ Partials        541      538       -3

Impacted Files	Coverage Δ	Complexity Δ
src/main/java/io/reactivex/Flowable.java	100% <ø> (ø)	566 <0> (ø)	⬇️
src/main/java/io/reactivex/Completable.java	100% <ø> (ø)	118 <0> (ø)	⬇️
src/main/java/io/reactivex/Observable.java	100% <ø> (ø)	541 <0> (ø)	⬇️
src/main/java/io/reactivex/Single.java	100% <ø> (ø)	148 <0> (ø)	⬇️
src/main/java/io/reactivex/Maybe.java	100% <ø> (ø)	172 <0> (ø)	⬇️
...activex/internal/operators/single/SingleUsing.java	100% <100%> (ø)	4 <0> (ø)	⬇️
...reactivex/internal/operators/maybe/MaybeUsing.java	100% <100%> (ø)	4 <0> (ø)	⬇️
...vex/internal/operators/flowable/FlowableUsing.java	100% <100%> (ø)	2 <0> (ø)	⬇️
...ternal/operators/completable/CompletableUsing.java	100% <100%> (ø)	4 <0> (ø)	⬇️
...internal/operators/observable/ObservableUsing.java	100% <100%> (ø)	2 <0> (ø)	⬇️
... and 25 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 46b4ac8...7cdd508. Read the comment docs.