Rollup merge of #70437 - RalfJung:miri-saturate, r=hanna-kruppe
Rollup merge of #70437 - RalfJung:miri-saturate, r=hanna-kruppe

Miri float->int casts: be explicit that this is saturating

r? @hanna-kruppe
Cc https://github.com/rust-lang/miri/issues/1264

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