Decide hybrid SDK API marker for v9

As we mark more SDK surface `@ApiStatus.Internal` ahead of v9 package moves, some types/methods are still consumed by hybrid SDKs (Flutter, React Native, etc.) even when they are not customer-facing.

`@ApiStatus.Internal` alone does not distinguish hybrid-facing surface from pure SDK plumbing, so hybrid consumers can be broken by a later relocate/remove pass.

Known examples called out during review of the utils Internal pass:

* `io.sentry.util.LoadClass`
* `io.sentry.util.TracingUtils`

Context: NoOp stubs and most util helpers were recently marked Internal (getsentry/sentry-java#6016, getsentry/sentry-java#6017); hybrids were explicitly left unmarked for now.

Action taken on behalf of Nelson Osacky.

Start by reviewing the internal-marking changes referenced in getsentry/sentry-java#6016 and #6017, focusing on io.sentry.util.LoadClass and io.sentry.util.TracingUtils. Compare the treatment of NoOp stubs, util helpers, and hybrid SDK consumers, then define and apply a marker policy that distinguishes hybrid-facing surface from pure SDK plumbing.

索引モデルが issue の本文から書いたものです。