Auto merge of #30931 - oli-obk:trans_disr_newtype, r=arielb1

This is groundwork for #30587 (typestrong constant integrals), but imo it's a change that in itself is good, too, since we don't just juggle `u64`s around anymore.

`ty::Disr` will be changed to a `ConstInt` in #30587

diff --cc src/librustc_trans/trans/foreign.rs
Simple merge

diff --cc src/librustc_typeck/check/mod.rs
Simple merge