Update android templates to use target sdk 34 (#144641)

We should always target the newest, and 34 is the newest. This isn't a requirement yet (like it is for 33+) but presumably it will be made required in the nearish future.

dev/integration_tests/android_custom_host_app/SampleApp/build.gradle

@@ -15,7 +15,7 @@ android {
     defaultConfig {
         applicationId "io.flutter.add2app"
         minSdkVersion 21
-        targetSdkVersion 33
+        targetSdkVersion 34
         versionCode 1
         versionName "1.0"
     }

dev/integration_tests/android_host_app_v2_embedding/app/build.gradle

@@ -15,7 +15,7 @@ android {
     defaultConfig {
         applicationId "io.flutter.add2app"
         minSdkVersion 21
-        targetSdkVersion 33
+        targetSdkVersion 34
         versionCode 1
         versionName "1.0"
     }

dev/integration_tests/module_host_with_custom_build_v2_embedding/app/build.gradle

@@ -15,7 +15,7 @@ android {
     defaultConfig {
         applicationId "io.flutter.addtoapp"
         minSdkVersion 21
-        targetSdkVersion 33
+        targetSdkVersion 34
         versionCode 1
         versionName "1.0"
     }

packages/flutter_tools/gradle/src/main/groovy/flutter.groovy

@@ -53,7 +53,7 @@ class FlutterExtension {
      *
      * See https://developer.android.com/guide/topics/manifest/uses-sdk-element.
      */
-    public final int targetSdkVersion = 33
+    public final int targetSdkVersion = 34
 
     /**
      * Sets the ndkVersion used by default in Flutter app projects.

packages/flutter_tools/lib/src/android/gradle_utils.dart

@@ -41,7 +41,7 @@ const String templateKotlinGradlePluginVersion = '1.7.10';
 // Please see the README before changing any of these values.
 const String compileSdkVersion = '34';
 const String minSdkVersion = '21';
-const String targetSdkVersion = '33';
+const String targetSdkVersion = '34';
 const String ndkVersion = '23.1.7779620';