Associate valid SpanId/SpanContext with Spans irrespective of the Sampling decision.

[lalitb]

Fixes #878

Changes

As per Specs, non-sampled / dropped spans should still have the valid SpanId. The child span of the non-sampled span should have the same trace_id associated.

Generate a new span ID for the Span, independently of the sampling decision. This is done so other components (such as logs or exception handling) can rely on a unique span ID, even if the Span is a non-recording instance.

This PR ensures that a valid span-id is associated with the non-sampled spans.

Please provide a brief description of the changes here.

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]

Codecov Report

Merging #879 (fc7247c) into main (8556485) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #879      +/-   ##
==========================================
+ Coverage   95.44%   95.45%   +0.02%     
==========================================
  Files         157      157              
  Lines        6633     6655      +22     
==========================================
+ Hits         6330     6352      +22     
  Misses        303      303              

Impacted Files	Coverage Δ
api/include/opentelemetry/trace/noop.h	86.21% <100.00%> (+1.60%)	⬆️
api/test/trace/noop_test.cc	100.00% <100.00%> (ø)
sdk/src/trace/tracer.cc	87.50% <100.00%> (+0.41%)	⬆️
sdk/test/trace/tracer_test.cc	99.46% <100.00%> (+0.01%)	⬆️