build: add luals check

This automatically downloads and uses the correct luals binary for the
currently used system. `make luals` will run luals on all lua files in
`runtime`.

We download lua-language-server manually instead of relying on
contributors downloading it on their own (like with stylua) as
lua-language-server is updated frequently which may cause unnecessary
friction. Therefore, we download a pinned version of luals which we then
can manually bump when needed. This can be re-evaluated if luals becomes
more stable in the future.

Currently this is not run when using `make lint` since cmake style "file
caching" doesn't seem possible at the moment. This is because checking a
single file doesn't seem to work.

Work on https://github.com/neovim/neovim/issues/24563.

runtime/autoload/ccomplete.lua

@@ -5,7 +5,8 @@
 
 -- Ignore "value assigned to a local variable is unused" because
 --  we can't guarantee that local variables will be used by plugins
--- luacheck: ignore 311
+-- luacheck: ignore
+--- @diagnostic disable
 
 local vim9 = require('_vim9script')
 local M = {}