Rollup merge of #121731 - oli-obk:eager_opaque_checks, r=compiler-errors

Now that inlining, mir validation and const eval all use reveal-all, we won't be constraining hidden types here anymore

r? `@compiler-errors`

one bubble down, two more to go

the test is unrelated, just something I noticed would be good to test in both the old solver and the new.

Author: Nadrieril