Add animated cursor support

Adds support for animated cursors on Cocoa, Wayland, Win32, and X11.

testcursor can take a semicolon separated list of filenames and load an animated cursor from them.

src/dynapi/SDL_dynapi.sym

@@ -1266,6 +1266,7 @@ SDL3_0.0.0 {
     SDL_SavePNG;
     SDL_GetSystemPageSize;
     SDL_GetPenDeviceType;
+    SDL_CreateAnimatedCursor;
     # extra symbols go here (don't modify this line)
   local: *;
 };