feat(filetype): support scripts.vim with filetype.lua (neovim#17517)

When filetype.vim is disabled, create the autocommand that runs
scripts.vim in filetype.lua.

Author: gpanders

runtime/filetype.lua

@@ -7,6 +7,7 @@ if vim.g.do_filetype_lua ~= 1 then
   return
 end
 
+-- TODO: Remove vim.cmd once Lua autocommands land
 vim.cmd [[
 augroup filetypedetect
 au BufRead,BufNewFile * call v:lua.vim.filetype.match(expand('<afile>'))
@@ -18,6 +19,12 @@ runtime! ftdetect/*.lua
 " Set a marker so that the ftdetect scripts are not sourced a second time by filetype.vim
 let g:did_load_ftdetect = 1
 
+" If filetype.vim is disabled, set up the autocmd to use scripts.vim
+if exists('did_load_filetypes')
+  au BufRead,BufNewFile * if !did_filetype() && expand('<amatch>') !~ g:ft_ignore_pat | runtime! scripts.vim | endif
+  au StdinReadPost * if !did_filetype() | runtime! scripts.vim | endif
+endif
+
 augroup END
 ]]