Problem:
`vim.pos.cursor(vim.api.nvim_get_current_buf(win), vim.api.nvim_win_get_cursor(win))`
is too verbose to create a cursor position of a window,
but it is a common use case.
Solution:
Overload `vim.pos.cursor()`, so that it accepts `win` as an argument when `pos` is omitted.
2bd13177b8
