Rollup merge of #91075 - jsha:chill-item-info, r=GuillaumeGomez

Rollup merge of #91075 - jsha:chill-item-info, r=GuillaumeGomez

Reduce prominence of item-infos

Fixes #59853

 - Remove border.
 - Reduce size of emoji slightly.
 - Remove details disclosure for unstable reason. This was inconsistent with our other details disclosures, and the detail revealed was usually better explained by clicking on the issue link.

Demo: https://rustdoc.crud.net/jsha/chill-item-info/std/mem/union.MaybeUninit.html#method.slice_assume_init_ref

Compare vs: https://doc.rust-lang.org/nightly/std/mem/union.MaybeUninit.html#method.slice_assume_init_ref

<img src="https://user-images.githubusercontent.com/220205/142717815-09828c9e-6ff4-445a-8ccc-31e028fd4985.png" width=700>