[feat request] Show trait info in LSP completion

[LittleJianCH]

It will be much helpful to show the trait info in LSP completion.

For example, there's a function write_object:

pub fn Logger::write_object[Obj : Show](self : Logger, obj : Obj) -> Unit {
  obj.output(self)
}

Now, LSP will show info like this

It's unhelpful since I don't what Obj is here. I have to jump to the definition of Logger::write_object to get enough informations.