feat(aucmd_win): allow crazy things with hidden buffers (#21250)

Problem:    Crash when doing crazy things with hidden buffers.
Solution:   Dynamically allocate the list of autocommand windows.

src/nvim/main.c

@@ -251,8 +251,6 @@ int main(int argc, char **argv)
   // `argc` and `argv` are also copied, so that they can be changed.
   init_params(&params, argc, argv);
 
-  autocmd_init();
-
   // Since os_open is called during the init_startuptime, we need to call
   // fs_init before it.
   fs_init();