chore(auth): delete 35 unreferenced fui_ string resources and their translations

[demolaf]

• Related to feat(lint): flag localized strings that still hold the base English text #2520

Deletes 35 fui_* string resources that nothing in :auth references, and their 2,687 translations across 84 locale folders.

Changes

• Removes the 35 declarations and every locale copy. History splits them into 18 speculative strings from feat: Accessibility & i18n Audit #2258 and 17 pre-Compose leftovers, none held back for planned work.
• Drops feat(lint): flag localized strings that still hold the base English text #2520's provisional fui_mfa_method_sms allowlist entry, added there on the basis that this PR would delete the string.
• Removes one stale lint-baseline.xml entry, and the tools:text attribute that was the only thing referencing fui_welcome_back_password_prompt_body.

Why this is not marked breaking

These are public resource surface, but the README documents overriding these names rather than reading them, and an override of a name the library no longer declares still compiles.

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Maintainer note: Fixes internal CPRN-445

[gemini-code-assist]

Code Review

This pull request refactors error message resolution in FirebaseUI Auth by mapping specific Firebase error codes to distinct exceptions and localized strings, while removing unused progress dialog strings across numerous localization files. It also updates the TopLevelDialogController to resolve strings dynamically from LocalAuthUIStringProvider. Feedback on these changes includes a recommendation to provide a default implementation for the new passwordTooLong method in AuthUIStringProvider to prevent breaking external implementations, and a suggestion to extract the digit regex in firstNumberIn to a companion object constant to optimize performance.

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auth/src/main/java/com/firebase/ui/auth/configuration/string_provider/AuthUIStringProvider.kt (187-188)

Adding a new abstract method passwordTooLong to the public interface AuthUIStringProvider is a breaking change for any external clients implementing this interface. To maintain backward compatibility, we should provide a default implementation (e.g., returning an empty string ""), which will automatically fall back to the default/English string without breaking compilation for existing custom implementations.

    /** Error message when the password is longer than the maximum length allowed. Should support string formatting with maximum length parameter. */
    fun passwordTooLong(maximumLength: Int): String = ""

auth/src/main/java/com/firebase/ui/auth/AuthException.kt (1022-1023)

To avoid compiling the regular expression pattern \d+ on every invocation of firstNumberIn, we should extract it as a private constant DIGIT_REGEX in the companion object. This improves performance and avoids unnecessary object allocation.

        private val DIGIT_REGEX = Regex("\\d+")

        private fun firstNumberIn(text: String): Int? =
            DIGIT_REGEX.find(text)?.value?.toIntOrNull()