Rollup merge of rust-lang#144209 - scottmcm:assume_less, r=lcnr,dianqk

Don't emit two `assume`s in transmutes when one is a subset of the other

For example, transmuting between `bool` and `Ordering` doesn't need two `assume`s because one range is a superset of the other.

Multiple are still used for things like `char` <-> `NonZero<u32>`, which overlap but where neither fully contains the other.

Author: matthiaskrgr