Add full support for Android scoped storage.

This was done by refactoring directory and file access handling for the Android platform so that any general filesystem access type go through the Android layer.
This allows us to validate whether the access is unrestricted, or whether it falls under scoped storage and thus act appropriately.

platform/android/java/editor/build.gradle

@@ -23,8 +23,7 @@ android {
         versionCode getGodotLibraryVersionCode()
         versionName getGodotLibraryVersionName()
         minSdkVersion versions.minSdk
-        //noinspection ExpiredTargetSdkVersion - Restrict to version 29 until https://github.com/godotengine/godot/pull/51815 is submitted
-        targetSdkVersion 29 // versions.targetSdk
+        targetSdkVersion versions.targetSdk
 
         missingDimensionStrategy 'products', 'editor'
     }