[core] Create spans using automatic span propagation

[maorleger]

Packages impacted by this PR

@azure/core-rest-pipeline
@typespec/ts-http-runtime

Issues associated with this PR

N/A

Describe the problem that is addressed by this PR

Back when we were migrating to the new core tracing we wanted to be cautious and
bail as early as possible in our core tracing policy. This meant that we:

1. Guard against any errors
2. Ignore automatic span propagation, instead expecting HLC libraries to call
   tracingClient.withSpan to kick off the manual span propagation (context
   parameter passing in options)

Now that we have RLC which does not have a tracingClient, and having had this
code in production for quite some time, we can remove the optimization that
aassumes the tracingContext will be added upstream.

This is a non-impactful change for high-level clients or anyone who has not opted-in to OTel tracing.

For users who use rest-level clients and have opted into OTel, they will now see HTTP spans from core added correctly

Are there test cases added in this PR? (If not, why?)

Updated test expectation

Provide a list of related PRs (if any)

Command used to generate this PR: (Applicable only to SDK release request PRs)

Checklists

• Added impacted package name to the issue description.
• Does this PR need any fixes in the SDK Generator?** (If so, create an Issue in the Autorest/typescript repository and link it here.)
• Added a changelog (if necessary).

[lmolkova]

Thank you!

[azure-sdk]

API change check

API changes are not detected in this pull request.