Auto merge of #31450 - bluss:no-null-markers, r=Gankro
Auto merge of #31450 - bluss:no-null-markers, r=Gankro

Document that Unique<T> and Shared<T> are non-null

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