Android: Enable backup of external app-specific directory

Source/Android/app/src/main/AndroidManifest.xml

@@ -1,5 +1,4 @@
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
-    xmlns:tools="http://schemas.android.com/tools"
     package="org.dolphinemu.dolphinemu">
 
     <uses-feature
@@ -30,13 +29,15 @@
         android:name="android.permission.VIBRATE"
         android:required="false"/>
 
+    <!-- Once compileSdkVersion is 31, add: android:dataExtractionRules="@xml/backup_rules_api_31" -->
     <application
         android:name=".DolphinApplication"
         android:label="@string/app_name"
         android:icon="@drawable/ic_launcher"
         android:requestLegacyExternalStorage="true"
         android:preserveLegacyExternalStorage="true"
-        android:allowBackup="false"
+        android:allowBackup="true"
+        android:fullBackupContent="@xml/backup_rules"
         android:supportsRtl="true"
         android:isGame="true"
         android:banner="@drawable/banner_tv">

Source/Android/app/src/main/res/xml/backup_rules.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="utf-8"?>
+<full-backup-content>
+    <include domain="external" path="."/>
+
+    <exclude domain="external" path="./Cache/"/>
+</full-backup-content>

Source/Android/app/src/main/res/xml/backup_rules_api_31.xml

@@ -0,0 +1,17 @@
+<?xml version="1.0" encoding="utf-8"?>
+<data-extraction-rules>
+    <cloud-backup disableIfNoEncryptionCapabilities="false">
+        <include domain="external" path="."/>
+
+        <exclude domain="external" path="./Cache/"/>
+        <exclude domain="external" path="./Dump/"/>
+        <exclude domain="external" path="./Load/"/>
+        <exclude domain="external" path="./ResourcePacks/"/>
+    </cloud-backup>
+
+    <device-transfer>
+        <include domain="external" path="."/>
+
+        <exclude domain="external" path="./Cache/"/>
+    </device-transfer>
+</data-extraction-rules>