Use a base path of "./" on Android

This allows filesystem operations to use internal storage and the asset system by default.

include/SDL3/SDL_filesystem.h

@@ -77,6 +77,8 @@ extern "C" {
  * - `parent`: the containing directory of the bundle. For example:
  *   `/Applications/SDLApp/`
  *
+ * **Android Specific Functionality**: This function returns "./", which allows filesystem operations to use internal storage and the asset system.
+ *
  * **Nintendo 3DS Specific Functionality**: This function returns "romfs"
  * directory of the application as it is uncommon to store resources outside
  * the executable. As such it is not a writable directory.