chore: do not export singletons

[dyladan]

Fixes #38

[codecov]

Codecov Report

Merging #46 (40e151f) into main (4cda9bd) will decrease coverage by 0.04%.
The diff coverage is 88.88%.

@@            Coverage Diff             @@
##             main      #46      +/-   ##
==========================================
- Coverage   94.70%   94.66%   -0.05%     
==========================================
  Files          42       42              
  Lines         567      562       -5     
  Branches       94       94              
==========================================
- Hits          537      532       -5     
  Misses         30       30              

Impacted Files	Coverage Δ
src/index.ts	100.00% <ø> (ø)
src/propagation/NoopTextMapPropagator.ts	71.42% <ø> (-3.58%)	⬇️
src/trace/NoopTracer.ts	95.65% <ø> (-0.10%)	⬇️
src/trace/NoopTracerProvider.ts	80.00% <50.00%> (-3.34%)	⬇️
src/api/propagation.ts	100.00% <100.00%> (ø)
src/trace/ProxyTracer.ts	100.00% <100.00%> (ø)
src/trace/ProxyTracerProvider.ts	93.33% <100.00%> (+0.47%)	⬆️

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[Flarna]

I know that the headline tells do not export singletons. But above I read ... does not require that we export any no-op classes or singletons.

Currently NoopTextMapPropagator, NoopTracer,.. are still exported. Shoudl we remove them also?

[Flarna]

I guess the followup PR in core will be funny :o).

[obecny]

it looks fine, but before this one is merged, we should first update core and contrib to avoid problems with being unable to make a release of those packages for a long time. Merging this PR should be a last thing in this task