Filter and/or de-prioritize trait names in expression context completion

[lnicola]

See #12123 (comment).

[Veykril]

*Only for traits that don't have assoc items though.

[lnicola]

It might still make sense to move down traits without associated constants, since it's not that common to invoke methods like that.

[Veykril]

I wouldn't be so sure about that, Default::default() is very common, From::from/Into::into also sees some use

[flodiebold]

I wonder, it might be nice to automatically complete Default::default() etc. for traits like this? I.e. have a completion for the full method call?

[flodiebold]

Or maybe we should just complete Default::$0 instead of Default -- that would apply to all traits in this position 🤔

But for traits with just one member just providing the full thing might still be better.

This should all be configurable though, since I'm sure there are people who will be annoyed by it...

[Veykril]

Ye I think those are some good ideas 👍

[lnicola]

Mostly fixed.