Rollup merge of #71165 - lcnr:patch-2, r=Amanieu
Rollup merge of #71165 - lcnr:patch-2, r=Amanieu

`slice::fill`: use `T` instead of generic arg

implements https://github.com/rust-lang/rust/issues/70758#issuecomment-613994427

As the discussion in #70758 has shifted, I now use `T` instead of `&T`.

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