feat(tracing): Add @sentry-internal/tracing package

[timfish]

Ref #5815.

This PR adds the internal @sentry-internal/tracing package.

A later PR will move the code from @sentry/tracing into this new package and re-export the types without causing any breaking changes.

[AbhiPrasad]

We'll also have to update .craft.yml as per https://github.com/getsentry/sentry-javascript/blob/develop/docs/new-sdk-release-checklist.md

[timfish]

Those docs say:

Before the Release:
2) Make sure that the new SDK is not added in craft.yml as a target for the Sentry release registry

After the Release
2) Add an entry to craft.yml to add releases of your SDK to the Sentry release registry

You did suggest previously that we don't add this new package to the registry.

[AbhiPrasad]

you are totally right Tim, we don't need this - I'm in too many places at once 😅

Thanks for the reminder!