ddtrace/tracer/textmap: always extract baggage when using w3c for compatability

[ajgajg1134]

What does this PR do?

With the new default of preferring w3c headers, if a user were to receive datadog baggage items they were lost as the w3c extract would successfully pull the trace id and other information but skip the baggage

Motivation

Closes #1752
The RFC states we should do this too:

If the Datadog tracing library previously propagated ot-baggage automatically via the Datadog propagator, then extract the ot-baggage header for OpenTracing baggage propagation.

Describe how to test/QA your changes

Added a unit test to cover this

Reviewer's Checklist

• If known, an appropriate milestone has been selected; otherwise the Triage milestone is set.
• Changed code has unit tests for its functionality.
• If this interacts with the agent in a new way, a system test has been added.

[pr-commenter]

Benchmarks

Comparing candidate commit 2697f0d in PR branch andrew.glaude/BaggageInW3c with baseline commit d343e64 in branch main.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 6 cases.