chore: upgrading to api ver. 0.20.0

[obecny]

• Upgrade to latest api 0.20

Ignore Tracer.ts -> startActiveSpan, I just took it from api, but once this PR is reviewed and merged ->
#2221
It will supersede the one I added (copy paste from api)

[codecov]

Codecov Report

Merging #2225 (e624704) into main (eb9353a) will decrease coverage by 0.43%.
The diff coverage is 65.15%.

@@            Coverage Diff             @@
##             main    #2225      +/-   ##
==========================================
- Coverage   92.72%   92.28%   -0.44%     
==========================================
  Files         142      142              
  Lines        5124     5146      +22     
  Branches     1050     1062      +12     
==========================================
- Hits         4751     4749       -2     
- Misses        373      397      +24     

Impacted Files	Coverage Δ
...ges/opentelemetry-exporter-zipkin/src/transform.ts	100.00% <ø> (ø)
...s/opentelemetry-instrumentation-fetch/src/fetch.ts	96.98% <ø> (ø)
...elemetry-tracing/src/export/ConsoleSpanExporter.ts	78.57% <ø> (ø)
packages/opentelemetry-tracing/src/Tracer.ts	67.14% <8.00%> (-32.86%)	⬇️
...e/src/baggage/propagation/HttpBaggagePropagator.ts	96.96% <100.00%> (ø)
...metry-core/src/trace/HttpTraceContextPropagator.ts	100.00% <100.00%> (ø)
...metry-core/src/trace/sampler/ParentBasedSampler.ts	83.87% <100.00%> (ø)
.../opentelemetry-exporter-collector/src/transform.ts	88.69% <100.00%> (ø)
...ges/opentelemetry-exporter-jaeger/src/transform.ts	100.00% <100.00%> (ø)
...elemetry-instrumentation-grpc/src/grpc-js/index.ts	90.81% <100.00%> (ø)
... and 9 more

[dyladan]

Thanks this looks like it was quite a bit of work.

[weyert]

Looks goods to me

[Flarna]

Suggested change

	readonly spanContext: () => SpanContext;
	spanContext(): SpanContext;

I find this more readable and it is in sync with the API Span interface

[Flarna]

Seems some lint setting has change recently. Same on a few other places.

I don't care much about this so feel free to keep.