fix(extui): close cmdwin to enter "more" window (#33860)

Problem:  Cannot enter "more" window while cmdwin is open since it is a
          regular window and changing windows is disallowed.
Solution: Close cmdwin to enter the "more" window. Minor regression
          w.r.t. the current message grid. Resolving that will require
          somehow bypassing textlock for the "more" window.

runtime/lua/vim/_extui/messages.lua

@@ -405,6 +405,14 @@ function M.set_pos(type)
       local row = (texth.all > height and texth.end_row or 0) + 1
       api.nvim_win_set_cursor(ext.wins[ext.tab].box, { row, 0 })
     elseif type == 'more' and api.nvim_get_current_win() ~= win then
+      -- Cannot leave the cmdwin to enter the "more" window, so close it.
+      -- NOTE: regression w.r.t. the message grid, which allowed this. Resolving
+      -- that would require somehow bypassing textlock for the "more" window.
+      if fn.getcmdwintype() ~= '' then
+        api.nvim_command('quit')
+      end
+      -- It's actually closed one event iteration later so schedule in case it was open.
+      vim.schedule(function()
         api.nvim_create_autocmd('WinEnter', {
           once = true,
           callback = function()
@@ -413,9 +421,10 @@ function M.set_pos(type)
             end
             append_more = 0
           end,
-        desc = 'Hide inactive more window.',
+          desc = 'Hide inactive "more" window.',
         })
         api.nvim_set_current_win(win)
+      end)
     end
   end