[Feature Request] forEachBaggageItems on SpanContext

[meteorlxy]

Implementations of many other languages have something like forEachBaggageItems on SpanContext:

• go: https://github.com/opentracing/opentracing-go/blob/master/span.go#L21
• java: https://github.com/opentracing/opentracing-java/blob/2df2a8983e35dff23c4fb894e5f5ae3f98f1cf7b/opentracing-api/src/main/java/io/opentracing/SpanContext.java#L59
• cpp: https://github.com/opentracing/opentracing-cpp/blob/7b8c0b30a26b138dbed714cde8347a0f5f2e060e/include/opentracing/span.h#L27

However, js does not:

https://github.com/opentracing/opentracing-javascript/blob/cb74683fefe5bd4d711eaa0c273f3fc17a6c3781/src/span_context.ts#L11-L33