`i_<M-CR>` does not work in original vim

The default insert-mode mapping for "run command and create new line for commands" is `i_<M-CR>`.

Original vim can not map Alt like that -- it just receives `<Esc>` plus whatever key is pressed.
Hence the above keybinding does not work for original vim.

Would be nice to think of some alternate keybinding which works for both neovim and original vim.