Rollup merge of #66410 - RalfJung:miri-machine-max, r=oli-obk
Rollup merge of #66410 - RalfJung:miri-machine-max, r=oli-obk

miri: helper methods for max values of machine's usize/isize

We recently wanted this in Miri.

r? @oli-obk

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