Discussion/Feature: highlight unused function argument as comment

[Simerax]

Since gleam supports prefixing an argument with underscore to mark it as unused it would be nice if the variable was highlighted like a comment.
The Elixir plugin vim-elixir does exactly that.

I hacked something together with my non existing vim regex skills:

What's the general opinion on this?

[lpil]

Sounds good to me!