Update to SDL 2.24.0 and add separate macOS UB2 dylib

Update mingw and macOS SDL libraries to 2.24.0. (MSVC .lib files and
Xcode project haven't been updated.)

There is now a separate SDL dylib for macOS Universal Binary 1 and 2
because SDL 2.24.0 dropped support for macOS 10.6 (which is last to
support x86). Documentation says SDL 2.24.0 also dropped macOS 10.7
and 10.8 too. So UB2 is now 10.9 or later while 10.5 to 10.8 live in
UB1.

Compiled using osxcross with macOS 11.3 SDK. Ran "strip -x" on Windows
and macOS libraries. Ad-hoc signed dylib using PyOxidizer rcodesign to
fix digest checksums after strip.

code/SDL2/include/SDL_touch.h

@@ -1,6 +1,6 @@
 /*
   Simple DirectMedia Layer
-  Copyright (C) 1997-2020 Sam Lantinga <slouken@libsdl.org>
+  Copyright (C) 1997-2022 Sam Lantinga <slouken@libsdl.org>
 
   This software is provided 'as-is', without any express or implied
   warranty.  In no event will the authors be held liable for any damages
@@ -64,30 +64,78 @@ typedef struct SDL_Finger
 #define SDL_MOUSE_TOUCHID ((Sint64)-1)
 
 
-/* Function prototypes */
-
 /**
- *  \brief Get the number of registered touch devices.
+ * Get the number of registered touch devices.
+ *
+ * On some platforms SDL first sees the touch device if it was actually used.
+ * Therefore SDL_GetNumTouchDevices() may return 0 although devices are
+ * available. After using all devices at least once the number will be
+ * correct.
+ *
+ * This was fixed for Android in SDL 2.0.1.
+ *
+ * \returns the number of registered touch devices.
+ *
+ * \since This function is available since SDL 2.0.0.
+ *
+ * \sa SDL_GetTouchDevice
  */
 extern DECLSPEC int SDLCALL SDL_GetNumTouchDevices(void);
 
 /**
- *  \brief Get the touch ID with the given index, or 0 if the index is invalid.
+ * Get the touch ID with the given index.
+ *
+ * \param index the touch device index
+ * \returns the touch ID with the given index on success or 0 if the index is
+ *          invalid; call SDL_GetError() for more information.
+ *
+ * \since This function is available since SDL 2.0.0.
+ *
+ * \sa SDL_GetNumTouchDevices
  */
 extern DECLSPEC SDL_TouchID SDLCALL SDL_GetTouchDevice(int index);
 
 /**
- * \brief Get the type of the given touch device.
+ * Get the touch device name as reported from the driver or NULL if the index
+ * is invalid.
+ *
+ * \since This function is available since SDL 2.0.22.
+ */
+extern DECLSPEC const char* SDLCALL SDL_GetTouchName(int index);
+
+/**
+ * Get the type of the given touch device.
+ *
+ * \since This function is available since SDL 2.0.10.
  */
 extern DECLSPEC SDL_TouchDeviceType SDLCALL SDL_GetTouchDeviceType(SDL_TouchID touchID);
 
 /**
- *  \brief Get the number of active fingers for a given touch device.
+ * Get the number of active fingers for a given touch device.
+ *
+ * \param touchID the ID of a touch device
+ * \returns the number of active fingers for a given touch device on success
+ *          or 0 on failure; call SDL_GetError() for more information.
+ *
+ * \since This function is available since SDL 2.0.0.
+ *
+ * \sa SDL_GetTouchFinger
  */
 extern DECLSPEC int SDLCALL SDL_GetNumTouchFingers(SDL_TouchID touchID);
 
 /**
- *  \brief Get the finger object of the given touch, with the given index.
+ * Get the finger object for specified touch device ID and finger index.
+ *
+ * The returned resource is owned by SDL and should not be deallocated.
+ *
+ * \param touchID the ID of the requested touch device
+ * \param index the index of the requested finger
+ * \returns a pointer to the SDL_Finger object or NULL if no object at the
+ *          given ID and index could be found.
+ *
+ * \since This function is available since SDL 2.0.0.
+ *
+ * \sa SDL_RecordGesture
  */
 extern DECLSPEC SDL_Finger * SDLCALL SDL_GetTouchFinger(SDL_TouchID touchID, int index);