refactor: move statusline code from buffer.c and [draw]screen.c to new file

problem: code for drawing statusline is arbitrarily spreadout between drawscreen.c, screen.c and buffer.c
solution: move it to a new file statusline.c

- rename archaic internal name "status match" to public name "wildmenu"
- showruler() does not show the ruler. it show anything which displays
  info about the cursor. Rename it accordingy.

src/nvim/ex_cmds.c

@@ -3976,7 +3976,7 @@ static int do_sub(exarg_T *eap, proftime_T timeout, long cmdpreview_ns, handle_T
                         _("replace with %s (y/n/a/q/l/^E/^Y)?"), sub);
               msg_no_more = false;
               msg_scroll = (int)i;
-              showruler(true);
+              show_cursor_info(true);
               ui_cursor_goto(msg_row, msg_col);
               RedrawingDisabled = temp;