fix(api): use active context as default in NoopTracer

[Flarna]

Which problem is this PR solving?

API without SDK usecase (only proagator and context manager and maybe some instrumentations used) doesn't work is one relies on context manager.

Short description of the changes

To support the API without SDK use cast to forward a span context it's needed to fetch active context via ContextManager also in NoopTracer. Otherwise only direct passing of a context works but not if context.with() is used.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

added unittest

Checklist:

• Followed the style guidelines of this project
• Unit tests have been added
• Documentation has been updated

[codecov]

Codecov Report

Merging #3476 (85e008d) into main (263ee61) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3476      +/-   ##
==========================================
- Coverage   93.77%   93.76%   -0.02%     
==========================================
  Files         248      248              
  Lines        7567     7567              
  Branches     1580     1581       +1     
==========================================
- Hits         7096     7095       -1     
- Misses        471      472       +1     

Impacted Files	Coverage Δ
api/src/trace/NoopTracer.ts	97.29% <100.00%> (ø)
...-trace-base/src/platform/node/RandomIdGenerator.ts	87.50% <0.00%> (-6.25%)	⬇️