[CODE HEALTH] Fix bugprone-exception-escape in NoopTracer::StartSpan()

[marcalff]

Contributes to #2053

Changes

Please provide a brief description of the changes here.

• Remove NoopSpan::tracer_, this property is unused
• Remove the tracer parameter from the NoopSpan constructor
• Adjusted all callers accordingly
• Add a NoopTracer::noop_span_ property
• Return the pre allocated NoopTracer::noop_span_ from NoopTracer::StartSpan(), fixing the issue.
• Added a CHANGELOG breaking change entry
• Added details in CHANGELOG for other PRs causing breaking changes

Please note:

• File api/include/opentelemetry/trace/noop.h is located under api.
• However, file noop.h is not part of the opentelemetry abi, as instrumented applications never see noop objects directly.
• Changing classes NoopSpan, NoopTracer and NoopTracerProvider is not a breaking change for instrumentation. It only affects custom exporters.

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

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.78%. Comparing base (cdb5e44) to head (7aa44c0).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4673      +/-   ##
==========================================
+ Coverage   86.77%   86.78%   +0.01%     
==========================================
  Files         525      525              
  Lines       20747    20742       -5     
==========================================
- Hits        18002    17998       -4     
+ Misses       2745     2744       -1     

Files with missing lines	Coverage Δ
api/include/opentelemetry/trace/noop.h	100.00% <100.00%> (ø)

... and 1 file with indirect coverage changes

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[dbarker]

Thanks. Please consider the optional changes below. Since this class may be instantiated by users and is in the public API, consider adding a breaking change entry to the CHANGELOG.