Auto merge of #160668 - sjwang05:next-solver-orphanck, r=lcnr

enable next solver by default in orphanck





Orphan checking was supposed to use next solver as well when `-Znext-solver=coherence` got stabilized, but it never actually did, so this PR fixes that as part of the effort here: [#t-types/call-for-participation > rip out old solver coherence support @ 💬](https://rust-lang.zulipchat.com/#narrow/channel/618216-t-types.2Fcall-for-participation/topic/rip.20out.20old.20solver.20coherence.20support/near/614920324)

also fixes rust-lang/rust#149703 and rust-lang/rust#148621, incidentally!

r? lcnr