Refactor string extensions

[Kielek]

Fixes #2919.

Changes

Remove extensions methods related to the BCL (string!) classes to reduce noisy in IntelliSense.

For significant contributions please make sure you have completed the following items:

• Appropriate CHANGELOG.md updated for non-trivial changes
• Design discussion issue Remove extensions method from BCL classes #2919
• Changes in public API reviewed

[codecov]

Codecov Report

Merging #3306 (14cd22c) into main (292b416) will decrease coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #3306      +/-   ##
==========================================
- Coverage   85.48%   85.43%   -0.05%     
==========================================
  Files         263      264       +1     
  Lines        9505     9505              
==========================================
- Hits         8125     8121       -4     
- Misses       1380     1384       +4     

Impacted Files	Coverage Δ
...TelemetryProtocol/OtlpExporterOptionsExtensions.cs	97.72% <ø> (-0.15%)	⬇️
...Telemetry.Exporter.Jaeger/JaegerExporterOptions.cs	100.00% <100.00%> (ø)
...ry.Exporter.Jaeger/JaegerExporterProtocolParser.cs	100.00% <100.00%> (ø)
....OpenTelemetryProtocol/OtlpExportProtocolParser.cs	100.00% <100.00%> (ø)
...orter.OpenTelemetryProtocol/OtlpExporterOptions.cs	100.00% <100.00%> (ø)
...ZPages/Implementation/ZPagesExporterEventSource.cs	56.25% <0.00%> (-6.25%)	⬇️
...ter.ZPages/Implementation/ZPagesActivityTracker.cs	97.14% <0.00%> (-2.86%)	⬇️
...nTelemetry/Internal/OpenTelemetrySdkEventSource.cs	73.27% <0.00%> (-0.87%)	⬇️
...Telemetry/Internal/SelfDiagnosticsEventListener.cs	96.87% <0.00%> (-0.79%)	⬇️

[reyang]

LGTM.