fix(api/buffer): fix handling of viewport of non-current buffer

A lot of functions in move.c only worked for curwin, alternatively
took a `wp` arg but still only work if that happens to be curwin.

Refactor those that are needed for update_topline(wp) to work
for any window.

fixes #27723
fixes #27720

src/nvim/ex_cmds2.c

@@ -654,7 +654,7 @@ void ex_listdo(exarg_T *eap)
       }
 
       if (eap->cmdidx == CMD_windo && execute) {
-        validate_cursor();              // cursor may have moved
+        validate_cursor(curwin);              // cursor may have moved
         // required when 'scrollbind' has been set
         if (curwin->w_p_scb) {
           do_check_scrollbind(true);