fix(auth): replace hardcoded loading state strings with translatable string resources

[demolaf]

Closes #2338 .

All AuthState.Loading messages emitted during auth operations (sign-in, sign-out, delete, phone, email, etc.) were hardcoded English strings. This replaces every instance with a string resource lookup via Context.getString(R.string.fui_loading_*), making them overridable and translatable.

Usage

You can either override using strings.xml or through a custom AuthUIStringProvider, see below examples:

Using strings.xml:

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <string name="fui_loading_signing_in_anonymously" translatable="false">some random string here</string>
    <string name="fui_loading_deleting_account" translatable="false">some random string here</string>
</resources>

Using AuthUIStringProvider:

class CustomAuthUIStringProvider(
    private val defaultProvider: AuthUIStringProvider
) : AuthUIStringProvider by defaultProvider {
    override val loadingSigningInAnonymously: String
        get() = "Overriding signing in anonymously loading message..."
}

val customStringProvider = CustomAuthUIStringProvider(DefaultAuthUIStringProvider(applicationContext))

val configuration = authUIConfiguration {
    // ... (existing params)
    stringProvider = customStringProvider
}

Preview

override-loading-state-preview.webm

[demolaf]

/gemini review

[gemini-code-assist]

Code Review

This pull request replaces hardcoded English loading messages with localized string resources across various authentication providers and operations (such as signing in, signing out, and deleting accounts). It also introduces new loading state properties to AuthUIStringProvider and its default implementation, along with corresponding unit tests. The review feedback suggests utilizing the custom stringProvider from the available config object instead of directly calling context.getString(...) or app.applicationContext.getString(...) in several provider helper files, ensuring that any user-supplied custom string provider is properly respected.

[mikehardy]

implementation looks really sound
my comments are informational as I don't know how strongly google style guide applies here and how deep the testing contract is - certainly the tests prove the general paths as is

[mikehardy]

similarly, the style guide has opinions on abbreviations. This one is likely a grey area. Is TOTP familiar to the audience? To us yes, but to mass consumers...possibly not? This abbreviation my be better as something like "Enter one time code" or something?

https://developers.google.com/style/abbreviations#spelling-out

[demolaf]

hmmm that's a valid point