test-app: adopt built-in Kotlin on Android, opt out of the AGP 9 DSL

With React Native 0.87 the test app builds against AGP 9.2.1, where
built-in Kotlin is enabled by default. Nothing in the build needs the
Kotlin plugin any more: ReactAndroid dropped it upstream,
react-native-test-app's modules are gated on it, and react-native-node-api
now only applies it when built-in Kotlin is unavailable. So unlike the
React Native app template, we do not set `android.builtInKotlin=false`.

The new DSL is a different matter and stays opted out: both of
react-native-test-app's Gradle modules still use the old one, and that is
third-party code. AGP 10 removes this opt out, so it is tracked in #389
along with the upstream code that has to migrate first.

Also pins the Gradle wrapper at 9.4.1, which react-native-test-app rewrites
it to at run time for React Native >= 0.87 — pinning it ourselves keeps CI
from building with a dirty working tree.

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

Author: kraenhansen

apps/test-app/android/gradle.properties

@@ -50,4 +50,16 @@ react.buildFromSource=true
 #ANDROID_NDK_VERSION=26.1.10909125
 
 # Version of Kotlin to build against.
-#KOTLIN_VERSION=1.8.22
+#KOTLIN_VERSION=1.8.22
+
+# Opt out of the new DSL that ships enabled in AGP 9, because both of
+# react-native-test-app's Gradle modules still use the old one. AGP 10 removes
+# this opt out, so it is on borrowed time — tracked in
+# https://github.com/callstackincubator/react-native-node-api/issues/389, which
+# links the upstream code that has to migrate first.
+#
+# Note that we deliberately do NOT opt out of built-in Kotlin (the flag AGP 10
+# also removes): React Native's own ReactAndroid no longer applies the Kotlin
+# plugin, and `react-native-node-api` only applies it when built-in Kotlin is
+# unavailable, so the whole build is built-in-Kotlin native.
+android.newDsl=false

apps/test-app/android/gradle/wrapper/gradle-wrapper.properties

@@ -1,6 +1,6 @@
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-9.3.1-bin.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-9.4.1-bin.zip
 networkTimeout=10000
 validateDistributionUrl=true
 zipStoreBase=GRADLE_USER_HOME