Support variable (or at least $HOME) expansion in languages.toml

[rouge8]

Some language servers, like typescript-language-server and vuels require specifying paths to plugins, e.g.:

[[language-server.typescript-language-server.config.plugins]]
name = "@vue/typescript-plugin"
location = "/Users/andy/.local/share/mise/installs/npm-vue-language-server/latest/lib/node_modules/@vue/language-server"
languages = [ "vue" ]

This works fine on one machine, but when I share the config across multiple machines with different usernames or OSes, I need to replace /Users/andy/ with $HOME. It would be super helpful to expand $HOME here (e.g. %{env.HOME} or similar) so users only need to maintain one config file.

[rouge8]

I came up with rouge8/dotfiles@39899b9 as a workaround.