feat(build): migrate to declarative Gradle plugin DSL and bump Dart SDK constraint to >=3.0.0 <4.0.0

android/app/build.gradle

@@ -1,3 +1,10 @@
+plugins {
+    id "com.android.application"
+    id "kotlin-android"
+    id "dev.flutter.flutter-gradle-plugin"
+    id "com.google.gms.google-services"
+}
+
 def localProperties = new Properties()
 def localPropertiesFile = rootProject.file('local.properties')
 if (localPropertiesFile.exists()) {
@@ -6,11 +13,6 @@ if (localPropertiesFile.exists()) {
     }
 }
 
-def flutterRoot = localProperties.getProperty('flutter.sdk')
-if (flutterRoot == null) {
-    throw new GradleException("Flutter SDK not found. Define location with flutter.sdk in the local.properties file.")
-}
-
 def flutterVersionCode = localProperties.getProperty('flutter.versionCode')
 if (flutterVersionCode == null) {
     flutterVersionCode = '1'
@@ -21,13 +23,6 @@ if (flutterVersionName == null) {
     flutterVersionName = '1.0'
 }
 
-apply plugin: 'com.android.application'
-// START: FlutterFire Configuration
-apply plugin: 'com.google.gms.google-services'
-// END: FlutterFire Configuration
-apply plugin: 'kotlin-android'
-apply from: "$flutterRoot/packages/flutter_tools/gradle/flutter.gradle"
-
 android {
     namespace "com.oggauergemeindetrommler.app"
     compileSdkVersion flutter.compileSdkVersion
@@ -75,6 +70,4 @@ flutter {
     source '../..'
 }
 
-dependencies {
-    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
-}
+dependencies {}