vim-patch:9.1.1779: completion: 'autocomplete' cannot be enabled per buffer (#35853)

Problem:  completion: 'autocomplete' cannot be enabled per buffer
          (Tomasz N)
Solution: Make 'autocomplete' global or local to buffer (Girish Palya)

fixes: vim/vim#18320
closes: vim/vim#18333

0208b3e80a

Co-authored-by: Girish Palya <girishji@gmail.com>

src/nvim/options.lua

@@ -236,7 +236,7 @@ local options = {
         |i_CTRL-N|, but triggered automatically.  See |ins-autocompletion|.
       ]=],
       full_name = 'autocomplete',
-      scope = { 'global' },
+      scope = { 'global', 'buf' },
       short_desc = N_('automatic completion in insert mode'),
       type = 'boolean',
       varname = 'p_ac',