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

[jj22ee]

lgtm!

[majanjua-amzn]

Looks like there's some transient failures in the PR build workflows, would appreciate some help with closing this out, thanks!

[pichlermarc]

proxy-approving for @jj22ee (component-owner)

Sorry for taking so long to merge this in - if there's any owner-approved PR that has been sitting for a while, please feel free to ping the approvers group to merge it :)

[otelbot]

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