Show individual `From`s in completion

[caojinyu]

In Rust, a large number of From traits are implemented for types. However, when we write code, Rust-analyzer will not automatically highlight all the specific types.

Can we achieve something like the effect of RustRover?

[ChayimFriedman2]

I'm not sure this is better. It consumes a lot of precious completion items.

[lnicola]

It does, but I think it's very nice for discoverability.