events: Add integer wheel fields for sdl2-compat

It's way simpler to just add them back to SDL3 than emulate them purely in sdl2-compat.

(cherry picked from commit 0447c2f3c3)

include/SDL3/SDL_events.h

@@ -492,6 +492,8 @@ typedef struct SDL_MouseWheelEvent
     SDL_MouseWheelDirection direction; /**< Set to one of the SDL_MOUSEWHEEL_* defines. When FLIPPED the values in X and Y will be opposite. Multiply by -1 to change them back */
     float mouse_x;      /**< X coordinate, relative to window */
     float mouse_y;      /**< Y coordinate, relative to window */
+    Sint32 integer_x;   /**< The amount scrolled horizontally, accumulated to whole scroll "ticks" (added in 3.2.12) */
+    Sint32 integer_y;   /**< The amount scrolled vertically, accumulated to whole scroll "ticks" (added in 3.2.12) */
 } SDL_MouseWheelEvent;
 
 /**