Rollup merge of #136890 - saethlin:swap_nonoverlapping, r=RalfJung

Change swap_nonoverlapping from lang to library UB

The implementation of ptr::swap_nonoverlapping does not always escalate its safety contract to language UB, so it should be `check_library_ub`.

Fixes rust-lang/miri#4188

Author: GuillaumeGomez