[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)

TODOs

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

cc: @walterjgsp

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[ncooke3]

I'll refactor this further in a following PR. It more easily reviewable now as it's a direct port of the ObjC bridge logic.

[ncooke3]

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

[ncooke3]

TODO: update with final Recaptcha version

[paulb777]

And the Recaptcha non-beta version publishing gates the merge.

[ncooke3]

when recaptcha SDK is released:

Suggested change

	// let client = try await recaptcha.fetchClient(withSiteKey: siteKey)
	let client = try await recaptcha.getClient(withSiteKey: siteKey)
	let client = try await recaptcha.fetchClient(withSiteKey: siteKey)

[paulb777]

Thanks for getting rid of the ObjC!