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/lua/vim/shared.lua

@@ -7,7 +7,7 @@
 -- so this wouldn't be a separate case to consider)
 
 ---@nodoc
-_G.vim = _G.vim or {}
+_G.vim = _G.vim or {} --[[@as table]] -- TODO(lewis6991): better fix for flaky luals
 
 ---@generic T
 ---@param orig T