File dialog improvements

- Add a globally-accessible function to handle the parsing of filter extensions
- Remove the ability of putting the wildcard ('*') among other patterns; it's either a list of patterns or a single '*' now
- Add a hint to select between portals and Zenity on Unix

include/SDL3/SDL_hints.h

@@ -414,6 +414,26 @@ extern "C" {
  */
 #define SDL_HINT_JOYSTICK_DIRECTINPUT "SDL_JOYSTICK_DIRECTINPUT"
 
+/**
+ * A variable that specifies a dialog backend to use.
+ *
+ * By default, SDL will try all available dialog backends in a reasonable order until it finds one that can work, but this hint allows the app or user to force a specific target.
+ *
+ * If the specified target does not exist or is not available, the dialog-related function calls will fail.
+ *
+ * This hint currently only applies to platforms using the generic "Unix" dialog implementation, but may be extended to more platforms in the future. Note that some Unix and Unix-like platforms have their own implementation, such as macOS and Haiku.
+ *
+ * The variable can be set to the following values:
+ *   NULL          - Select automatically (default, all platforms)
+ *   "portal"      - Use XDG Portals through DBus (Unix only)
+ *   "zenity"      - Use the Zenity program (Unix only)
+ *
+ * More options may be added in the future.
+ *
+ * This hint can be set anytime.
+ */
+#define SDL_HINT_FILE_DIALOG_DRIVER "SDL_FILE_DIALOG_DRIVER"
+
 /**
  * Override for SDL_GetDisplayUsableBounds()
  *