Rollup merge of #44477 - napen123:master, r=frewsxcv
Rollup merge of #44477 - napen123:master, r=frewsxcv

Add doc examples to str::from_utf8_unchecked_mut

Fixes #44461

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