Add partial support for Android scoped storage.

This is done by providing API access to app specific directories which don't have any limitations and allows us to bump the target sdk version to 30.
In addition, we're also bumping the min sdk version to 19 as version 18 is no longer supported by Google Play Services and only account of 0.3% of Android devices.

platform/android/java/app/AndroidManifest.xml

@@ -22,6 +22,7 @@
         android:icon="@mipmap/icon"
         android:isGame="true"
         android:hasFragileUserData="false"
+        android:requestLegacyExternalStorage="false"
         tools:ignore="GoogleAppIndexingWarning" >
 
         <!-- Records the version of the Godot editor used for building -->

platform/android/java/app/config.gradle

@@ -1,8 +1,8 @@
 ext.versions = [
-    androidGradlePlugin: '4.2.1',
-    compileSdk         : 29,
-    minSdk             : 18,
-    targetSdk          : 29,
+    androidGradlePlugin: '4.2.2',
+    compileSdk         : 30,
+    minSdk             : 19,
+    targetSdk          : 30,
     buildTools         : '30.0.3',
     supportCoreUtils   : '1.0.0',
     kotlinVersion      : '1.5.10',