time: Use a function instead of properties to retrieve the system date and time locale info

This allows applications to re-query the values if the system locale is changed during runtime, and better matches the other locale functions. A note is included in the documentation mentioning that this can be slow, as it has to call into OS functions.

Also allows for the removal of the init/quit time functions, as they are no longer needed.

src/dynapi/SDL_dynapi.sym

@@ -1015,6 +1015,7 @@ SDL3_0.0.0 {
     SDL_wcsnstr;
     SDL_wcsstr;
     SDL_wcstol;
+    SDL_GetDateTimeLocalePreferences;
     # extra symbols go here (don't modify this line)
   local: *;
 };