Auto merge of #103690 - GuillaumeGomez:visibility-on-demand, r=notriddle

Make rustdoc Item::visibility computed on-demand

This is a take-over of rust-lang/rust#91408.

Helps with rust-lang/rust#90852 (needs to use `ty::Visibility` directly too).

cc `@camelid`
r? `@notriddle`

Author: bors