[Auth] Add support for upcoming Recaptcha changes

[ncooke3]

Corresponding PR for google/interop-ios-for-google-sdks#16 that is backwards compatible for Recaptcha ≤18.6 (edit: backwards compatible is not needed due to dependency versioning)

Support Cases

1. Old Recaptcha x Old Firebase → ✅ Will continue to work, no changes
2. Old Recaptcha x New Firebase → ❌ Won't work because of conflicting recaptcha interop dependency
3. New Recaptcha x Old Firebase → ❌ Won't work because of conflicting recaptcha interop dependency
4. New Recaptcha x New Firebase → ✅ Will work bc of this PR

Testing (manual tests– is reCaptcha token generated?)

• CocoaPods - dynamic linking
• CocoaPods - static linking
• SPM manual test
• Zip manual test (will wait for new Recaptcha interop and Recaptcha SDK to be released)
• SPM: try await Auth.auth().initializeRecaptchaConfig() throws error when Recaptcha is not linked

TODOs

• Looking into the existing rCE unit test PRs to see if we can get unit tests checked in too

cc: @walterjgsp

[ncooke3]

Adding this to M158 milestone for consideration. Will probably slip to M159.

[paulb777]

Thanks for getting rid of the ObjC!

[ncooke3]

Moved back to a later milestone as new Recaptcha version is not yet released.

[ncooke3]

Moved back to a later milestone as new Recaptcha version is not yet released.