TESTWM : Option and Keyboard action to ShowCursor and HideCursor

In include/SDL3/SDL_test_common.h
   Add flag hide_cursor
In src/test/SDL_test_common.c
   Handle option --hide-cursor to SDL_HideCursor
   Handle Ctrl-h toggle to SDL_HideCursor and SDL_ShowCursor

include/SDL3/SDL_test_common.h

@@ -127,6 +127,7 @@ typedef struct
 
     /* Mouse info */
     SDL_Rect confine;
+    SDL_bool hide_cursor;
 
 } SDLTest_CommonState;