android: Increase compileSdkVersion to 31 for all plugins

This commit updates the `compileSdkVersion` for all plugins to resolve the
`android:attr/lStar not found` error encountered during build. It adjusts the
compile SDK version to 31 to align with AndroidX dependencies and newer Android
SDK requirements. This change is made in the `subprojects` section of the
`android/build.gradle` file to ensure all plugins adhere to this version
without manual updates.

flutter/flutter#153281 (comment)

src/ui/flutter_app/android/build.gradle

@@ -7,8 +7,29 @@ allprojects {
 
 rootProject.buildDir = '../build'
 subprojects {
+    afterEvaluate { project ->
+        if (project.extensions.findByName("android") != null) {
+            Integer pluginCompileSdk = project.android.compileSdk
+            if (pluginCompileSdk != null && pluginCompileSdk < 31) {
+                project.logger.error(
+                        "Warning: Overriding compileSdk version in Flutter plugin: "
+                                + project.name
+                                + " from "
+                                + pluginCompileSdk
+                                + " to 31 (to work around https://issuetracker.google.com/issues/199180389)."
+                                + "\nIf there is not a new version of " + project.name + ", consider filing an issue against "
+                                + project.name
+                                + " to increase their compileSdk to the latest (otherwise try updating to the latest version)."
+                )
+                project.android {
+                    compileSdk 31
+                }
+            }
+        }
+    }
+
     project.buildDir = "${rootProject.buildDir}/${project.name}"
-    project.evaluationDependsOn(':app')
+    project.evaluationDependsOn(":app")
 }
 
 tasks.register("clean", Delete) {