fix(ui2): entering the pager fails if <ESC> is remapped to :fclose (#39462)

Problem:  Entering the pager fails if <ESC> is remapped to :fclose by user.
Solution: Avoid executing mappings with nvim_feedkeys() that closes expanded cmdline.
(cherry picked from commit 2b7a00746d)

runtime/lua/vim/_core/ui2/messages.lua

@@ -600,7 +600,7 @@ local function enter_pager()
   if was_cmdwin ~= '' then
     api.nvim_command('quit')
   elseif M.cmd_on_key then
-    api.nvim_feedkeys(vim.keycode('<Esc>'), 't', false)
+    api.nvim_feedkeys(vim.keycode('<Esc>'), 'tn', false)
   end
   -- Cmdwin is closed one event iteration later so schedule in case it was open.
   vim.schedule(function()

test/functional/ui/messages2_spec.lua

@@ -180,6 +180,7 @@ describe('messages2', function()
       foo [+9]                                             |
     ]])
     -- Do enter the pager in normal mode.
+    command('nmap <Esc> <Cmd>fclose<CR>')
     feed('<CR>')
     screen:expect([[
       ^foo                                                  |