RUM-2568: Better handling of event write errors in RUM

[0xnm]

What does this PR do?

This PR improves any error handling in the write pipeline of RUM. Before, if there was any exception thrown inside writing pipeline which wasn't caught, or if write wasn't successful, we didn't notify that event wasn't written (or dropped, in other words). This prevented to decrease pendingXXX counters in RumViewScope, thus making isComplete to evaluate to false in such cases.

This PR also centralizes the place where the notification about write success or failure is sent.

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• Make sure you discussed the feature or bugfix with the maintaining team in an Issue
• Make sure each commit and the PR mention the Issue number (cf the CONTRIBUTING doc)

[codecov-commenter]

Codecov Report

Merging #1766 (54d41c6) into develop (3947313) will increase coverage by 0.04%.
The diff coverage is 91.93%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1766      +/-   ##
===========================================
+ Coverage    83.64%   83.68%   +0.04%     
===========================================
  Files          465      466       +1     
  Lines        16336    16364      +28     
  Branches      2454     2452       -2     
===========================================
+ Hits         13664    13694      +30     
+ Misses        2018     2017       -1     
+ Partials       654      653       -1     

Files	Coverage Δ
...lin/com/datadog/android/rum/internal/RumFeature.kt	93.49% <ø> (+0.63%)	⬆️
...tadog/android/rum/internal/domain/RumDataWriter.kt	100.00% <100.00%> (+7.14%)	⬆️
...ndroid/rum/internal/domain/event/RumEventMapper.kt	100.00% <100.00%> (+4.62%)	⬆️
...kotlin/com/datadog/android/rum/utils/SdkCoreExt.kt	97.44% <97.44%> (ø)
...ndroid/rum/internal/domain/scope/RumActionScope.kt	97.18% <95.52%> (+0.66%)	⬆️
...roid/rum/internal/domain/scope/RumResourceScope.kt	95.17% <94.81%> (+0.49%)	⬆️
.../android/rum/internal/domain/scope/RumViewScope.kt	93.76% <88.97%> (-0.38%)	⬇️

... and 10 files with indirect coverage changes

[xgouchet]

Niceliy done !