Auto merge of #34745 - alexandermerritt:slice-doc, r=brson
Auto merge of #34745 - alexandermerritt:slice-doc, r=brson

make docs for clone_from_slice consistent with copy_from_slice

What 'this slice' refers to is not intuitive, given this method can appear in other places, e.g. in docs for Vec.

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