RUMM-2834: Tracing feature stores context in the common context storage

[0xnm]

What does this PR do?

This change makes tracing feature to store its context (active span) in the common context storage.

The tricky part is that active span (span backed by the current active scope) is thread-local, so each thread may have its own active span. To support such thread-local storage I'm using addScopeListener API to associate the active context with the particular thread and then later to read it from DatadogContext for the particular thread as well (reminder: DatadogContext is created on the caller thread).

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 #1216 (3eaf25d) into feature/sdkv2 (62fa834) will increase coverage by 0.08%.
The diff coverage is 92.31%.

@@                Coverage Diff                @@
##           feature/sdkv2    #1216      +/-   ##
=================================================
+ Coverage          82.67%   82.75%   +0.08%     
=================================================
  Files                353      353              
  Lines              12576    12589      +13     
  Branches            2086     2087       +1     
=================================================
+ Hits               10397    10418      +21     
+ Misses              1541     1528      -13     
- Partials             638      643       +5     

Impacted Files	Coverage Δ
.../kotlin/com/datadog/android/v2/api/FeatureScope.kt	50.00% <ø> (ø)
...otlin/com/datadog/android/tracing/AndroidTracer.kt	92.94% <85.71%> (-1.43%)	⬇️
...android/log/internal/domain/DatadogLogGenerator.kt	97.04% <100.00%> (+0.09%)	⬆️
...n/com/datadog/android/v2/core/SdkInternalLogger.kt	88.89% <0.00%> (-5.56%)	⬇️
...src/main/kotlin/com/datadog/android/DatadogSite.kt	83.33% <0.00%> (-3.33%)	⬇️
...in/com/datadog/android/log/internal/LogsFeature.kt	85.38% <0.00%> (-3.08%)	⬇️
...droid/rum/tracking/ActivityViewTrackingStrategy.kt	86.54% <0.00%> (-1.92%)	⬇️
...core/internal/system/DefaultAndroidInfoProvider.kt	83.02% <0.00%> (-1.89%)	⬇️
.../android/rum/internal/monitor/DatadogRumMonitor.kt	90.81% <0.00%> (-0.54%)	⬇️
.../kotlin/com/datadog/android/v2/core/DatadogCore.kt	85.89% <0.00%> (-0.40%)	⬇️
... and 8 more

[mariusc83]

Nice work !!

[mariusc83]

yes...this is what we needed