vim-patch:8.2.3627: difficult to know where the text starts in a window (#16377)

vim-patch:8.2.3627: difficult to know where the text starts in a window

Problem:    difficult to know where the text starts in a window. (Sergey
            Vlasov)
Solution:   Add the "textoff" entry in the result of getwininfo().
            (closes vim/vim#9163)
cdf5fdb294

Fix indent in Test_getbufwintabinfo().

runtime/doc/eval.txt

@@ -5562,6 +5562,9 @@ getwininfo([{winid}])					*getwininfo()*
 					otherwise
 			wincol		leftmost screen column of the window;
 					"col" from |win_screenpos()|
+			textoff		number of columns occupied by any
+					'foldcolumn', 'signcolumn' and line
+					number in front of the text
 			winid		|window-ID|
 			winnr		window number
 			winrow		topmost screen line of the window;