Rollup merge of #105455 - lcnr:correct-reveal-in-validate, r=jackh726

use the correct `Reveal` during validation

supersedes #105454. Deals with rust-lang/rust#105009 (comment), not closing #105009 as the ICE may leak into beta

The issue was the following:
- we optimize the mir, using `Reveal::All`
- some optimization relies on the hidden type of an opaque type
- we then validate using `Reveal::UserFacing` again which is not able to observe the hidden type

r? `@jackh726`