vim-patch:8.1.0815: dialog for file changed outside of Vim not tested (#28184)

Problem:    Dialog for file changed outside of Vim not tested.
Solution:   Add a test.  Move FileChangedShell test.  Add 'L' flag to
            feedkeys().

https://github.com/vim/vim/commit/5e66b42aae7c67a3ef67617d4bd43052ac2b73ce

Co-authored-by: Bram Moolenaar <Bram@vim.org>

test/old/testdir/test_buffer.vim

@@ -232,8 +232,6 @@ endfunc
 
 " Test for deleting a modified buffer with :confirm
 func Test_bdel_with_confirm()
-  " requires a UI to be active
-  throw 'Skipped: use test/functional/legacy/buffer_spec.lua'
   CheckUnix
   CheckNotGui
   CheckFeature dialog_con
@@ -251,8 +249,6 @@ endfunc
 
 " Test for editing another buffer from a modified buffer with :confirm
 func Test_goto_buf_with_confirm()
-  " requires a UI to be active
-  throw 'Skipped: use test/functional/legacy/buffer_spec.lua'
   CheckUnix
   CheckNotGui
   CheckFeature dialog_con