Rollup merge of #128453 - RalfJung:raw_eq, r=saethlin

raw_eq: using it on bytes with provenance is not UB (outside const-eval)

The current behavior of raw_eq violates provenance monotonicity. See rust-lang/rust#124921 for an explanation of provenance monotonicity. It is violated in raw_eq because comparing bytes without provenance is well-defined, but adding provenance makes the operation UB.

So remove the no-provenance requirement from raw_eq. However, the requirement stays in-place for compile-time invocations of raw_eq, that indeed cannot deal with provenance.

Cc `@rust-lang/opsem`

Author: matthiaskrgr