feat(TraceProvider): add shutdown and forceFlush to API

[secustor]

This PR exposes the shutdown and forcedFlush functions defined by the TraceProvider specs.

Providing these methods allow to gracefully shutdown instrumentations without data loss. Currently this is only possible with usage of the SDK specific implementations see

Context

Closes https://github.com/open-telemetry/opentelemetry-js-api/issues/34

[codecov[bot]]

Codecov Report

Merging #172 (302455d) into main (d2fb706) will decrease coverage by 0.54%. The diff coverage is 50.00%.

@@            Coverage Diff             @@
##             main     open-telemetry/opentelemetry-js-api#172      +/-   ##
==========================================
- Coverage   95.23%   94.68%   -0.55%     
==========================================
  Files          45       45              
  Lines         650      658       +8     
  Branches      102      102              
==========================================
+ Hits          619      623       +4     
- Misses         31       35       +4     

Impacted Files	Coverage Δ
src/trace/NoopTracerProvider.ts	80.00% <50.00%> (-20.00%)	:arrow_down:
src/trace/ProxyTracerProvider.ts	85.00% <50.00%> (-8.75%)	:arrow_down:

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[dyladan]

@secustor can you please re-apply this in https://github.com/open-telemetry/opentelemetry-js where this package is now moved?