RUM-6286: replacing joinToString when it possible, refactor a bit

[satween]

What does this PR do?

Here we're trying to reduce usages of joinToString method inside the project, replacing it with more performant string builder

Motivation

Using joinToString may cause a lot of memory and cpu consumption which we trying to avoid, minimizing impact of sdk to user's code

Additional Notes

Anything else we should know when reviewing?

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

Attention: Patch coverage is 95.83333% with 1 line in your changes missing coverage. Please review.

Project coverage is 69.95%. Comparing base (f9bc2b5) to head (b2a6eae).
Report is 10 commits behind head on develop.

Files with missing lines	Patch %	Lines
...droid/core/internal/data/upload/CurlInterceptor.kt	85.71%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2456      +/-   ##
===========================================
- Coverage    69.99%   69.95%   -0.04%     
===========================================
  Files          785      786       +1     
  Lines        29278    29279       +1     
  Branches      4884     4886       +2     
===========================================
- Hits         20491    20480      -11     
- Misses        7430     7441      +11     
- Partials      1357     1358       +1     

Files with missing lines	Coverage Δ
.../android/error/internal/DatadogExceptionHandler.kt	87.67% <100.00%> (-0.17%)	⬇️
...datadog/android/internal/utils/StringBuilderExt.kt	100.00% <100.00%> (ø)
...g/android/rum/internal/DatadogLateCrashReporter.kt	85.88% <ø> (+1.13%)	⬆️
...dog/android/rum/internal/anr/AndroidTraceParser.kt	92.45% <100.00%> (ø)
...adog/android/rum/internal/net/RumRequestFactory.kt	69.32% <100.00%> (+3.03%)	⬆️
...droid/core/internal/data/upload/CurlInterceptor.kt	82.35% <85.71%> (-2.26%)	⬇️

... and 26 files with indirect coverage changes

[0xnm]

I left few comments/suggestions. The only blocker for me is having new extension method in the core module instead of internal.