vim-patch:9.0.1503: Luau files are not recognized (#23412)

Problem:    Luau files are not recognized.
Solution:   Add a patter for Luau files. (Amaan Qureshi, closes vim/vim#12317)

2dcfe9ae1d

Co-authored-by: Amaan Qureshi <amaanq12@gmail.com>

runtime/lua/vim/filetype.lua

@@ -637,6 +637,7 @@ local extension = {
   nse = 'lua',
   rockspec = 'lua',
   lua = 'lua',
+  luau = 'luau',
   lrc = 'lyrics',
   m = function(path, bufnr)
     return require('vim.filetype.detect').m(bufnr)