Allow changing vsync and framerate limit at runtime

Also implements a new menu item flag: MENUITEMFLAG_SLIDER_DEFERRED,
which only calls the MENUOP_GETSLIDER callback on entering dimmed mode,
storing its value for later ticks, and only calls the MENUOP_SET
callback on leaving dimmed mode. This was necessary to prevent the
framerate limit slider from immediately affecting the framerate, leading
to an annoying slow down as the value was decremented to 0.

src/include/constants.h

@@ -1666,6 +1666,7 @@
 #define MENUITEMFLAG_CAROUSEL_04000000       0x04000000
 #define MENUITEMFLAG_LITERAL_TEXT            0x08000000
 #define MENUITEMFLAG_SLIDER_WIDE             0x10000000
+#define MENUITEMFLAG_SLIDER_DEFERRED         0x20000000
 
 #define MENUITEMTYPE_LABEL       0x01
 #define MENUITEMTYPE_LIST        0x02
@@ -1696,7 +1697,7 @@
 
 #ifndef PLATFORM_N64
 #define MENUITEMTYPE_COLORBOX    0x1b
-#endif 
+#endif
 
 #define MENUMODELFLAG_HASSCALE    0x01
 #define MENUMODELFLAG_HASPOSITION 0x02