[local_auth] Switch to Kotlin Pigeon

[stuartmorgan-g]

Replaces the Java Pigeon generator with the Kotlin Pigeon generator, and adjusts the project accordingly:

• Adds Kotlin build setings to Gradle.
• Updates API signatures for Kotlin/Java differences.
• Adds generic Java/Kotlin compat shim to create Result objects from Java, since those haven't been added to the Pigeon generator yet.
• Updates tests to use constructors instead of builders, since the Kotlin generator doesn't create builders.
• Updates tests to use a Java/Kotlin compat shim to read Kotlin Result values, instead of mocking the Java Pigeon response object.

Part of flutter/flutter#158287

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Footnotes

1. Regular contributors who have demonstrated familiarity with the repository guidelines only need to comment if the PR is not auto-exempted by repo tooling. ↩ ↩²

[stuartmorgan-g]

This was just an opportunistic fix while I was in the file; the IDE flagged that we never actually read this value (it's used in the constructor where it's passed in, but never outside that, so doesn't need to be stored).

[gemini-code-assist]

Code Review

This pull request updates the local_auth_android package to version 2.0.8, migrating the internal Pigeon implementation from Java to Kotlin. Key changes include updating the build configuration to target Java 17, replacing the generated Java Messages class with a Kotlin equivalent, and refactoring the plugin and its tests to use a new callback-based API. Feedback suggests adding @JvmName to the completeWithValue utility function to improve interoperability when called from Java code.

[gemini-code-assist]

When exposing Kotlin functions to Java that involve kotlin.Result in their signature (even as a type argument in a lambda), it is a best practice to use @JvmName to ensure the method names are not mangled by the Kotlin compiler and remain easily callable from Java. While mangling might not occur for Function1 type arguments in all Kotlin versions, explicitly naming them improves interoperability and prevents potential build issues in different environments.

Suggested change

	fun <T> completeWithError(callback: (Result<@JvmSuppressWildcards T>) -> Unit, failure: Throwable) {
	callback(Result.failure(failure))
	}
	fun <T> completeWithValue(callback: (Result<@JvmSuppressWildcards T>) -> Unit, value: T) {
	callback(Result.success(value))
	}
	fun <T> completeWithError(callback: (Result<@JvmSuppressWildcards T>) -> Unit, failure: Throwable) {
	callback(Result.failure(failure))
	}
	@JvmName("completeWithValue")
	fun <T> completeWithValue(callback: (Result<@JvmSuppressWildcards T>) -> Unit, value: T) {
	callback(Result.success(value))
	}

[mboetger]

nit: add /* biometrics */ like comments so we know what these values represent.

[stuartmorgan-g]

Done.

(Longer term we may add a Pigeon Kotlin generator option to generate builders, for a more Java-like experience when using it from Java code.)

[mboetger]

LGTM w/small nit