Rollup merge of #34749 - GuillaumeGomez:any_doc, r=steveklabnik
Rollup merge of #34749 - GuillaumeGomez:any_doc, r=steveklabnik

Improve std::any module doc

Fixes #29340.

r? @steveklabnik

GBGamer/rust,graydon/rust,GBGamer/rust,GBGamer/rust,GBGamer/rust,aidancully/rust,GBGamer/rust,GBGamer/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,GBGamer/rust,aidancully/rust,graydon/rust,GBGamer/rust,graydon/rust,graydon/rust