Add support for changing save location on Android (#1520)

- Enabled the Android UI path for changing the data folder
- Added Android MANAGE_EXTERNAL_STORAGE permission
- Added an Android flow to request “All files access” before opening the folder picker
- Added code path to resume the folder selection flow after returning from Android settings
- Improved the Android write-probe error message to point users at the required permission

src/dusk/data.cpp

@@ -525,7 +525,14 @@ bool validate_writable_data_path(const std::filesystem::path& path, std::string*
     try {
         io::FileStream::WriteAllText(probePath, "dusk");
     } catch (const std::exception& e) {
+#if defined(__ANDROID__)
+        set_error(errorOut,
+            fmt::format("{} could not write to the selected folder. On Android, allow "
+                        "\"All files access\" for Dusklight and try again.",
+                AppName));
+#else
         set_error(errorOut, fmt::format("{} could not write to the selected folder.", AppName));
+#endif
         Log.warn("Failed write probe for custom data folder '{}': {}", io::fs_path_to_string(path),
             e.what());
         return false;