fix(device_info_plus): apply KGP unless built-in Kotlin is enabled

The guard assumed AGP 9 always means built-in Kotlin is active. AGP enables
built-in Kotlin only when android.builtInKotlin is not explicitly false, and
`flutter create` writes android.builtInKotlin=false into every new app.

On AGP 9 with android.builtInKotlin=false, the plugin skipped KGP and AGP
provided no Kotlin either, so nothing compiled the plugin's Kotlin sources and
configuration failed at the KotlinAndroidProjectExtension lookup. This was
masked only because Flutter's kgpRegexKotlin does not match the imperative
apply(plugin = "...") form, so Flutter applied KGP as a fallback on the
plugin's behalf.

Guard on the same condition AGP itself uses: built-in Kotlin is on when
AGP >= 9 and android.builtInKotlin is not explicitly false.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: 4akloon

packages/device_info_plus/device_info_plus/android/build.gradle.kts

@@ -28,7 +28,13 @@ plugins {
 
 val agpMajor = com.android.Version.ANDROID_GRADLE_PLUGIN_VERSION.substringBefore('.').toInt()
 
-if (agpMajor < 9) {
+// AGP 9 provides Kotlin support natively unless the consuming app opts out with
+// android.builtInKotlin=false, which is what `flutter create` writes by default.
+val builtInKotlinEnabled =
+    agpMajor >= 9 &&
+        (providers.gradleProperty("android.builtInKotlin").orNull?.toBoolean() ?: true)
+
+if (!builtInKotlinEnabled) {
     apply(plugin = "org.jetbrains.kotlin.android")
 }