Improve docs around `Once::call_once_force` and `OnceState`.
Improve docs around `Once::call_once_force` and `OnceState`.

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