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 #9163)

runtime/doc/eval.txt

@@ -6382,6 +6382,9 @@ 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;

src/evalwindow.c

@@ -407,6 +407,7 @@ get_win_info(win_T *wp, short tpnr, short winnr)
 #endif
     dict_add_number(dict, "width", wp->w_width);
     dict_add_number(dict, "wincol", wp->w_wincol + 1);
+    dict_add_number(dict, "textoff", win_col_off(wp));
     dict_add_number(dict, "bufnr", wp->w_buffer->b_fnum);
 
 #ifdef FEAT_TERMINAL

src/testdir/test_bufwintabinfo.vim

@@ -50,6 +50,7 @@ func Test_getbufwintabinfo()
 
   only
   let w1_id = win_getid()
+  setl foldcolumn=3
   new
   let w2_id = win_getid()
   tabnew | let w3_id = win_getid()
@@ -68,6 +69,7 @@ func Test_getbufwintabinfo()
   call assert_equal(winbufnr(2), winlist[1].bufnr)
   call assert_equal(winheight(2), winlist[1].height)
   call assert_equal(1, winlist[1].wincol)
+  call assert_equal(3, winlist[1].textoff)  " foldcolumn
   call assert_equal(tablineheight + winheight(1) + 2, winlist[1].winrow)
 
   call assert_equal(1, winlist[2].winnr)

src/version.c

@@ -757,6 +757,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3627,
 /**/
     3626,
 /**/