2.x: Adjust JavaDoc stylesheet of dt/dd within the method details

[akarnokd]

This PR adjusts the JavaDoc stylesheet so that the dt/dd listings in the detailed method descriptions no longer use monospaced font (which should be generally reserved for {@code }s and {@link }`s) for better readability.

Before:

After:

[codecov]

Codecov Report

Merging #6102 into 2.x will increase coverage by 0.02%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##                2.x    #6102      +/-   ##
============================================
+ Coverage     98.24%   98.27%   +0.02%     
  Complexity     6197     6197              
============================================
  Files           667      667              
  Lines         44862    44862              
  Branches       6213     6213              
============================================
+ Hits          44075    44086      +11     
+ Misses          243      238       -5     
+ Partials        544      538       -6

Impacted Files	Coverage Δ	Complexity Δ
...l/operators/observable/ObservableFlatMapMaybe.java	89.54% <0%> (-2.62%)	2% <0%> (ø)
...tivex/internal/schedulers/TrampolineScheduler.java	96.1% <0%> (-2.6%)	6% <0%> (ø)
...ternal/operators/completable/CompletableMerge.java	96.42% <0%> (-2.39%)	2% <0%> (ø)
.../internal/disposables/ListCompositeDisposable.java	98% <0%> (-2%)	34% <0%> (-1%)
...rnal/operators/flowable/FlowableFlatMapSingle.java	92.93% <0%> (-1.64%)	2% <0%> (ø)
...rnal/operators/observable/ObservableSwitchMap.java	94.68% <0%> (-1.6%)	3% <0%> (ø)
...java/io/reactivex/processors/UnicastProcessor.java	98.8% <0%> (-1.2%)	67% <0%> (-1%)
...perators/mixed/ObservableSwitchMapCompletable.java	98.94% <0%> (-1.06%)	3% <0%> (ø)
...nternal/operators/observable/ObservableCreate.java	98.29% <0%> (-0.86%)	2% <0%> (ø)
.../operators/maybe/MaybeFlatMapIterableFlowable.java	97.54% <0%> (-0.82%)	2% <0%> (ø)
... and 19 more

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