code: def ensure_app_cache_dir(appname, *args):
      
      import utool as ut
      dpath = get_app_cache_dir(appname, *args)
      ut.ensuredir(dpath)
      return dpath
docs: Example:
          >>> # DISABLE_DOCTEST
          >>> from utool.util_cplat import *  # NOQA
          >>> import utool as ut
          >>> dpath = ut.ensure_app_cache_dir('utool')
          >>> assert exists(dpath)