docs(lua): add Lua 5.1 reference manual (#19663)

based on http://www.vim.org/scripts/script.php?script_id=1291
reformatted to match Nvim documentation style; removed irrelevant sections

Co-authored-by: dundargoc <gocundar@gmail.com>
Co-authored-by: Christian Clason <c.clason@uni-graz.at>
Co-authored-by: Lewis Russell <lewis6991@gmail.com>

runtime/lua/vim/shared.lua

@@ -526,7 +526,7 @@ function vim.trim(s)
   return s:match('^%s*(.*%S)') or ''
 end
 
---- Escapes magic chars in a Lua pattern.
+--- Escapes magic chars in |lua-patterns|.
 ---
 ---@see https://github.com/rxi/lume
 ---@param s string String to escape