add BITS associated constant to core::num::Wrapping
add BITS associated constant to core::num::Wrapping

This keeps `Wrapping` synchronized with the primitives it wraps as for
the #32463 `wrapping_int_impl` feature.

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