3.x: Update Gradle task dependencies to remove dependsOn 'build' task

[benjamintboyle]

It is generally discouraged to add dependencies on 'build', so 'javadocCleanup'
and 'jacocoTestReport' have been removed and put on better tasks. Also,
'jacocoTestReport' needs input from the test results.

Updated task dependencies:

• Gradle 'javadoc' task is finalized by 'javadocCleanup', and 'javadocCleanup'
  no longer directly invoked by 'build'
• Gradle 'jacocoTestReport' task run by 'check' instead of 'build', and
  'jacocoTestReport' depends on 'test' and 'testng'

Changes due to dependency updates:

• Add 'javadoc' generation task on Github actions that only 'build'
• Remove 'javadocCleanup' task from Github action as 'publish...' tasks
  already dependent on 'javadoc'

Miscellaneous tangential cleanup:

• Remove "pr" parameter on command line in Github workflow as parameter
  is no longer functional
• Enclose source/target compatibility in Gradle java block

[codecov]

Codecov Report

Merging #7255 (ad0ac6c) into 3.x (93e5216) will increase coverage by 0.00%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##                3.x    #7255   +/-   ##
=========================================
  Coverage     99.51%   99.51%           
  Complexity     6758     6758           
=========================================
  Files           747      747           
  Lines         47391    47391           
  Branches       6382     6382           
=========================================
+ Hits          47161    47162    +1     
- Misses          100      105    +5     
+ Partials        130      124    -6     

Impacted Files	Coverage Δ	Complexity Δ
...l/operators/observable/ObservableFlatMapMaybe.java	89.43% <0.00%> (-4.93%)	2.00% <0.00%> (ø%)
...tivex/rxjava3/internal/jdk8/ParallelCollector.java	93.57% <0.00%> (-4.59%)	2.00% <0.00%> (ø%)
...eactivex/rxjava3/processors/BehaviorProcessor.java	97.48% <0.00%> (-2.52%)	50.00% <0.00%> (ø%)
...nternal/operators/parallel/ParallelReduceFull.java	91.08% <0.00%> (-1.99%)	2.00% <0.00%> (ø%)
...internal/operators/flowable/FlowableFromArray.java	96.61% <0.00%> (-1.70%)	3.00% <0.00%> (ø%)
...3/internal/operators/observable/ObservableZip.java	99.31% <0.00%> (-0.69%)	6.00% <0.00%> (ø%)
...nternal/operators/observable/ObservableReplay.java	99.46% <0.00%> (-0.54%)	22.00% <0.00%> (ø%)
...ernal/operators/flowable/FlowableFlatMapMaybe.java	96.89% <0.00%> (-0.52%)	2.00% <0.00%> (ø%)
...a3/internal/operators/flowable/FlowableCreate.java	99.02% <0.00%> (-0.33%)	6.00% <0.00%> (ø%)
...3/internal/operators/flowable/FlowableGroupBy.java	85.02% <0.00%> (+0.29%)	3.00% <0.00%> (ø%)
... and 14 more

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