Problem: col() and charcol() only work for the current window.
Solution: Add an optional winid argument. (Yegappan Lakshmanan,
closesvim/vim#11466, closesvim/vim#11461)
4c8d2f02b3
Cherry-pick test_functions.vim change from patch 8.2.0633.
Co-authored-by: Yegappan Lakshmanan <yegappan@yahoo.com>