Removed temporary memory from the API

It was intended to make the API easier to use, but various automatic garbage collection all had flaws, and making the application periodically clean up temporary memory added cognitive load to using the API, and in many cases was it was difficult to restructure threaded code to handle this.

So, we're largely going back to the original system, where the API returns allocated results and you free them.

In addition, to solve the problems we originally wanted temporary memory for:
* Short strings with a finite count, like device names, get stored in a per-thread string pool.
* Events continue to use temporary memory internally, which is cleaned up on the next event processing cycle.

include/SDL3/SDL_guid.h

@@ -67,14 +67,14 @@ typedef struct SDL_GUID {
  * Get an ASCII string representation for a given SDL_GUID.
  *
  * \param guid the SDL_GUID you wish to convert to string.
- * \returns the string representation of the GUID or NULL on failure; call
- *          SDL_GetError() for more information.
+ * \param pszGUID buffer in which to write the ASCII string.
+ * \param cbGUID the size of pszGUID, should be at least 33 bytes.
  *
  * \since This function is available since SDL 3.0.0.
  *
  * \sa SDL_StringToGUID
  */
-extern SDL_DECLSPEC_TEMP const char * SDLCALL SDL_GUIDToString(SDL_GUID guid);
+extern SDL_DECLSPEC void SDLCALL SDL_GUIDToString(SDL_GUID guid, char *pszGUID, int cbGUID);
 
 /**
  * Convert a GUID string into a SDL_GUID structure.