Rollup merge of #81940 - jhpratt:stabilize-str_split_once, r=m-ou-se
Rollup merge of #81940 - jhpratt:stabilize-str_split_once, r=m-ou-se

Stabilize str_split_once

Closes #74773

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