Register opaque types even when equated with infer variables

[compiler-errors]

note: This doesn't work, but it does fix #99536. Just putting this code up for other people's eyes.

The issue this attempts to solve here is that when we Equate::tys on an inference variable and an opaque type, we end up just storing the opaque type in the type variable table, instead of handling the opaque type as we should be doing.

Thoughts on this? cc @oli-obk in particular. I'd like to work towards a real working solution if possible, if this approach has any merit.

[compiler-errors]

r? @oli-obk

[compiler-errors]

What the heck. Why did that commit get pushed, lol.

[compiler-errors]

There.

[compiler-errors]

But anyways it seems like the behavior chosen that this PR tries to "fix" was intentional. So, gonna close this.

[rust-log-analyzer]

The job mingw-check failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

    Checking rustc_monomorphize v0.0.0 (/checkout/compiler/rustc_monomorphize)
    Checking rustc_passes v0.0.0 (/checkout/compiler/rustc_passes)
    Checking rustc_ast_lowering v0.0.0 (/checkout/compiler/rustc_ast_lowering)
    Checking rustc_save_analysis v0.0.0 (/checkout/compiler/rustc_save_analysis)
error[E0609]: no field `infcx` on type `&mut Equate<'_, '_, 'tcx>`
  --> compiler/rustc_infer/src/infer/equate.rs:84:22
   |
84 |                 self.infcx.super_combine_tys(self, a, b)
   |
   |
   = note: available fields are: `fields`, `a_is_expected`
   |
   |
84 |                 self.fields.infcx.super_combine_tys(self, a, b)

    Checking rustc_resolve v0.0.0 (/checkout/compiler/rustc_resolve)
For more information about this error, try `rustc --explain E0609`.
error: could not compile `rustc_infer` due to previous error