Rollup merge of #111980 - compiler-errors:unmapped-substs, r=lcnr

Preserve substs in opaques recorded in typeck results

This means that we now prepopulate MIR with opaques with the right substs.

The first commit is a hack that I think we discussed, having to do with `DefiningAnchor::Bubble` basically being equivalent to `DefiningAnchor::Error` in the new solver, so having to use `DefiningAnchor::Bind` instead, lol.

r? `@lcnr`

Author: Dylan-DPC