fix(editorconfig): highlight properties with dashes (#24407)

also add metadata comment and update Lua code in syntax file

runtime/syntax/editorconfig.vim

@@ -1,15 +1,18 @@
+" Nvim syntax file
+" Language:     EditorConfig
+" Last Change:  2023-07-20
+"
+" This file is intentionally _not_ copied from Vim.
+
 runtime! syntax/dosini.vim
 unlet! b:current_syntax
 
-syntax match editorconfigUnknownProperty "^\s*\zs\w\+\ze\s*="
+syntax match editorconfigUnknownProperty "^\s*\zs[a-zA-Z0-9_-]\+\ze\s*="
 syntax keyword editorconfigProperty root
 
 lua<<
-local props = {}
-for k in pairs(require('editorconfig').properties) do
-  props[#props + 1] = k
-end
-vim.cmd(string.format('syntax keyword editorconfigProperty %s', table.concat(props, ' ')))
+local props = vim.tbl_keys(require('editorconfig').properties)
+vim.cmd.syntax { 'keyword', 'editorconfigProperty', unpack(props) }
 .
 
 hi def link editorconfigProperty dosiniLabel