[ETW exporter] - Remove reference of TracerProvider from Tracer

[lalitb]

Fixes # (issue)

Changes

Remove reference of exporter::etw::TracerProvider from exporter::etw::Tracer class. Similar to the OpenTelemetry SDK implementation, the Tracer and TracerProvide now share TracerContext object, which remains active for the lifetime of the Tracer object.

These changes are on top of #1547, as IDGenerator and Sampler also need to be shared across Tracer and TracerProvider.

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

• [ ] CHANGELOG.md updated for non-trivial changes
• [ ] Unit tests have been added
• [ ] Changes in public API reviewed

[codecov[bot]]

Codecov Report

Merging #1567 (fc3fc4c) into main (39d6a22) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #1567   +/-   ##
=======================================
  Coverage   85.02%   85.02%           
=======================================
  Files         156      156           
  Lines        4977     4977           
=======================================
  Hits         4231     4231           
  Misses        746      746           

[ThomsonTan]

@lalitb could you please resolve the conflicts?