Lifetime bounds missing from re-exported items in documentation

[tomjakubowski]

Given:

// foo.rs
pub struct Items<'a, T: 'a>;

// bar.rs
extern crate foo;
pub use foo::Items;

Documentation for bar.rs shows struct Items<'a, T>, missing the lifetime bound. This is still the case on my branch in #17798

[tomjakubowski]

Since I've just gotten myself waist-deep in this, I'll try to fix it in the coming days 😄