vim-patch:9.1.1127: preinsert text is not cleaned up correctly (#32544)

Problem:  when 'completeopt' is set to preinsert the preinserted text is
          not cleared when adding new leader (Yee Cheng Chin)
Solution: add a condition to delete preinsert text in edit function
          (glepnir)

closes: vim/vim#16672

52fd867f5e

Co-authored-by: glepnir <glephunter@gmail.com>

test/old/testdir/test_ins_complete.vim

@@ -3110,6 +3110,11 @@ function Test_completeopt_preinsert()
   call assert_equal("fobar", getline('.'))
   call assert_equal(5, col('.'))
 
+  set cot=preinsert
+  call feedkeys("Sfoo1 foo2\<CR>f\<C-X>\<C-N>bar", 'tx')
+  call assert_equal("fbar", getline('.'))
+  call assert_equal(4, col('.'))
+
   bw!
   set cot&
   set omnifunc&