Verify `autoInjectSentryLabel` works in Expo build pipeline

[antonis]

Expo uses babel.config.js rather than the Metro transformer path to configure the component annotate plugin. The #6098 autoInjectSentryLabel option needs to work in both flows.

What to verify:

1. Expo apps using the Sentry Expo plugin pick up the new option correctly
2. The sentry-label injection works at build time in an Expo managed workflow
3. The sentry-label injection works in an Expo bare workflow
4. No build errors or unexpected behavior

How to test:

• Use the Expo sample app at samples/expo/
• Enable autoInjectSentryLabel in the Babel config
• Build and verify that static text children produce sentry-label props at runtime

Could be combined with the Metro config enablement task or done as a separate verification pass.

[linear-code]

RN-616

[antonis]

Verified autoInjectSentryLabel works in the Expo build pipeline using the sample app at samples/expo/.

Test method: Ran npx expo export for both iOS and web platforms against main (which includes #6141).

Results:

• iOS bundle: sentry-label props injected via Metro transformer path — labels found (e.g. "sentry-label":"Modal", "sentry-label":"Tab Two This is unmasked because it's direct child of Sentry....")
• Web bundle: sentry-label props injected across route chunks — same labels present
• Component annotations (data-sentry-component) continue to work alongside sentry-label
• No build errors on either platform
• The ignoredComponents option passes through correctly

The Expo flow uses the same withSentryBabelTransformer → addSentryComponentAnnotatePlugin code path as plain RN, so autoInjectSentryLabel: true applies identically. No code changes needed.