fix(android): skip explicit Kotlin plugin when AGP registers the kotlin extension

AGP 9 ships built-in Kotlin support and registers the kotlin extension
itself. Applying the Kotlin plugin again fails configuration with
"Cannot add extension with name 'kotlin'". Check for the extension
directly, which needs no AGP version table and covers AGP 10, where the
android.builtInKotlin opt-out is removed.

Author: gabrieldonadel

android/build.gradle

@@ -19,7 +19,13 @@ def safeExtGet(prop, fallback) {
 
 apply plugin: "com.android.library"
 apply plugin: "com.facebook.react"
-apply plugin: "kotlin-android"
+// AGP 9 ships built-in Kotlin support and registers the `kotlin` extension
+// itself. Applying the Kotlin plugin on top of it fails configuration with
+// "Cannot add extension with name 'kotlin'". Only apply it when nothing has
+// registered that extension yet.
+if (project.extensions.findByName('kotlin') == null) {
+    apply plugin: "kotlin-android"
+}
 
 android {
     namespace "com.xmartlabs.line"