Migrate KSP off AGP's legacy Variant API

[scott-pollom]

AndroidPluginIntegration is using the deprecated AGP Variant API and should migrate to the new AGP Variant API.

E.g., KotlinJvmAndroidCompilation.androidVariant returns an instance of the deprecated com.android.build.gradle.api.BaseVariant.

[scott-pollom]

Related bug, blocking the migration for the usage in AndroidPluginIntegration::getCompilationSourceSets: https://issuetracker.google.com/issues/317215060

[scott-pollom]

Related bug, blocking the migration for the usage in AndroidPluginIntegration::getCompilationSourceSets: https://issuetracker.google.com/issues/317215060

The new API was added in AGP 8.9.0-alpha09, so KSP must update its AGP dependency to at least that version to migrate.

[Jolanrensen]

After this change (since version 1.0.30), KSP no longer works in our java-8 targeting library.

We're trying to target Kotlin 2.1.20, so the lowest available version is 1.0.31, which is past this change. I couldn't find a mention of a minimum JDK version for the gradle plugin anywhere, so I'd assume while Kotlin supports java 8, KSP would too.

[hungvietnguyen]

cc @ting-yuan

In AGP 9.0 (canaries coming soon), access to the old variant API will be disabled by default (https://developer.android.com/build/releases/gradle-plugin-roadmap), so it would be great to finish the migration away from the legacy variant API.

Also related bug in KGP: https://youtrack.jetbrains.com/issue/KT-77300/