feat: add composite propagator

[dyladan]

Which problem is this PR solving?

• Add specified Composite Propagator https://github.com/open-telemetry/opentelemetry-specification/blob/master/specification/api-propagators.md#composite-propagator

[codecov-io]

Codecov Report

Merging #821 into master will decrease coverage by 1.44%.
The diff coverage is 97.18%.

@@            Coverage Diff             @@
##           master     #821      +/-   ##
==========================================
- Coverage   94.13%   92.68%   -1.45%     
==========================================
  Files         249      247       -2     
  Lines       10751    10997     +246     
  Branches     1028     1071      +43     
==========================================
+ Hits        10120    10193      +73     
- Misses        631      804     +173

Impacted Files	Coverage Δ
...elemetry-core/src/context/propagation/composite.ts	100% <100%> (ø)
.../opentelemetry-core/test/context/composite.test.ts	96.36% <96.36%> (ø)
...s/opentelemetry-core/test/context/B3Format.test.ts	50% <0%> (-50%)	⬇️
packages/opentelemetry-core/test/utils/url.test.ts	50% <0%> (-50%)	⬇️
...pentelemetry-core/test/internal/validators.test.ts	50% <0%> (-50%)	⬇️
...elemetry-core/test/trace/spancontext-utils.test.ts	55.55% <0%> (-44.45%)	⬇️
...lemetry-core/test/trace/ProbabilitySampler.test.ts	56.52% <0%> (-43.48%)	⬇️
...s/opentelemetry-core/test/trace/tracestate.test.ts	65.06% <0%> (-34.94%)	⬇️
...ckages/opentelemetry-core/test/platform/id.test.ts	66.66% <0%> (-33.34%)	⬇️
...ntelemetry-core/test/trace/NoRecordingSpan.test.ts	71.42% <0%> (-28.58%)	⬇️
... and 38 more

[mayurkale22]

Please fix the build

[mayurkale22]

lgtm