fix(cmdline): wrong 'incsearch' highlighting after :redraw (#27947)

Problem:  Calling :redraw from a timer callback clears 'incsearch' highlighting.
Solution: Re-apply 'incsearch' highlighting if the screen was updated.

src/nvim/ex_getln.c

@@ -1167,6 +1167,7 @@ static int command_line_execute(VimState *state, int key)
     return -1;  // get another key
   }
 
+  disptick_T display_tick_saved = display_tick;
   CommandLineState *s = (CommandLineState *)state;
   s->c = key;
 
@@ -1178,6 +1179,10 @@ static int command_line_execute(VimState *state, int key)
     } else {
       map_execute_lua(false);
     }
+    // Re-apply 'incsearch' highlighting in case it was cleared.
+    if (display_tick > display_tick_saved && s->is_state.did_incsearch) {
+      may_do_incsearch_highlighting(s->firstc, s->count, &s->is_state);
+    }
 
     // nvim_select_popupmenu_item() can be called from the handling of
     // K_EVENT, K_COMMAND, or K_LUA.