Show `Trait Bound` in the function signature hints.

[lh123]

Currently, RA (Rust Analyzer) does not display Trait Bound in the function signature hints.

fn test<R: std::io::Read>(r: R)  {}
fn test1<R>(r: R) where R: std::io::Read {}

Current: (where R: std::io::Read not show)

Expected:
Show Trait Bound just like hover

[Veykril]

Sounds fine by me, but should be gated behind the signatureInfo.detail config as a new variant (without changing the current default)