Android: Enable backup of external app-specific directory

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>