Rollup merge of #34930 - frewsxcv:vec-as-slice, r=steveklabnik
Rollup merge of #34930 - frewsxcv:vec-as-slice, r=steveklabnik

Add doc examples for `Vec::{as_slice,as_mut_slice}`.

None

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