fix(android): skip explicit Kotlin plugin when AGP provides built-in Kotlin (#1058)

AGP 9 enables built-in Kotlin by default and applies the Kotlin plugin
itself. Applying it again fails configuration with "Cannot add extension
with name 'kotlin'". Guard the explicit apply so it only runs when AGP is
not providing Kotlin: AGP 8 and older, or AGP 9 with
android.builtInKotlin=false. AGP 10 removes that opt-out, so built-in
Kotlin is always active there and the explicit apply must never run.

Author: gabrieldonadel

android/build.gradle

@@ -18,7 +18,28 @@ def isNewArchitectureEnabled() {
 }
 
 apply plugin: 'com.android.library'
-apply plugin: 'org.jetbrains.kotlin.android'
+// Android Gradle Plugin 9 ships built-in Kotlin support and applies the Kotlin
+// plugin itself. Applying it a second time fails the configuration phase with
+// "Cannot add extension with name 'kotlin'". Apply it only when AGP is not
+// providing Kotlin: AGP 8 and older, or AGP 9 with android.builtInKotlin=false.
+def shouldApplyKotlinPlugin() {
+    def agpMajor = com.android.Version.ANDROID_GRADLE_PLUGIN_VERSION.tokenize('.')[0].toInteger()
+    if (agpMajor <= 8) {
+        return true
+    }
+    // AGP 10 removes the opt-out: built-in Kotlin is always active there.
+    if (agpMajor >= 10) {
+        return false
+    }
+    def propertyVal = providers.gradleProperty("android.builtInKotlin").orNull
+    def builtInKotlinEnabled = propertyVal != null ? propertyVal.toBoolean() : true
+    return !builtInKotlinEnabled
+}
+
+if (shouldApplyKotlinPlugin()) {
+    apply plugin: 'org.jetbrains.kotlin.android'
+}
+
 if (isNewArchitectureEnabled()) {
   apply plugin: "com.facebook.react"
 }