Added support for Motion JPEG camera capture

Fixes https://github.com/libsdl-org/SDL/issues/12183

include/SDL3/SDL_pixels.h

@@ -676,6 +676,9 @@ typedef enum SDL_PixelFormat
     SDL_PIXELFORMAT_EXTERNAL_OES = 0x2053454fu,     /**< Android video texture format */
         /* SDL_DEFINE_PIXELFOURCC('O', 'E', 'S', ' ') */
 
+    SDL_PIXELFORMAT_MJPG = 0x47504a4du,     /**< Motion JPEG */
+        /* SDL_DEFINE_PIXELFOURCC('M', 'J', 'P', 'G') */
+
     /* Aliases for RGBA byte arrays of color data, for the current platform */
     #if SDL_BYTEORDER == SDL_BIG_ENDIAN
     SDL_PIXELFORMAT_RGBA32 = SDL_PIXELFORMAT_RGBA8888,