fix: ensure aws-xray-propagator maintains trace state

[majanjua-amzn]

Which problem is this PR solving?

• AWSXRayPropagator doesn't inject or extract the OTel trace state appropriately, which makes the extracted span context default to an empty trace state.

Short description of the changes

• Update extract to extract the trace state from the context if available and update the returned context accordingly
• Updated comments/title of trace state injection test and created new unit test for extraction
• Updated CHANGELOG

[jj22ee]

I think the bot is responsible for updating this Changelog, so you'll need to undo this change.

[jj22ee]

Suggested change

	const finalSpanContext: SpanContext = existingTraceState
	? {
	...spanContext,
	traceState: existingTraceState,
	}
	: spanContext;
	return trace.setSpan(context, trace.wrapSpanContext(finalSpanContext));
	if (existingTraceState) {
	spanContext.traceState = existingTraceState
	}
	return trace.setSpan(context, trace.wrapSpanContext(spanContext));