Rollup merge of #117091 - compiler-errors:debug, r=lcnr

`OptWithInfcx` naming nits, trait bound simplifications

* Use an associated type `Interner` on `InferCtxtLike` to remove a redundant interner parameter (`I: Interner, Infcx: InferCtxtLike<I>` -> `Infcx: InferCtxtLike`).
* Remove double-`Option` between `infcx: Option<Infcx>` and `fn universe_of_ty(&self, ty: ty::InferTy) -> Option<ty::UniverseIndex>`. We don't need the infcx to be optional if we can provide a "noop" (`NoInfcx`) implementation that just always returns `None` for universe index.
    * Also removes the `core::convert::Infallible` implementation which I found a bit weird...
* Some naming nits with params.
    * I found `InferCtxt` + `InfCtx` and `Infcx` to be a lot of different ways to spell "inference context", so I got rid of the `InfCtx` type parameter name in favor of `Infcx` which is a more standard name.
    * I found `OptWithInfcx` to be a bit redundant -> `WithInfcx`.

I'm making these changes because I intend to reuse the `InferCtxtLike` trait for uplifting the canonicalizer into a new trait -- conveniently, the information I need for uplifting the canonicalizer also is just the universe information of a type var, so it's super convenient 😸

r? `@BoxyUwU` or `@lcnr`

compiler/rustc_infer/src/infer/mod.rs

@@ -341,7 +341,9 @@ pub struct InferCtxt<'tcx> {
     next_trait_solver: bool,
 }
 
-impl<'tcx> ty::InferCtxtLike<TyCtxt<'tcx>> for InferCtxt<'tcx> {
+impl<'tcx> ty::InferCtxtLike for InferCtxt<'tcx> {
+    type Interner = TyCtxt<'tcx>;
+
     fn universe_of_ty(&self, ty: ty::InferTy) -> Option<ty::UniverseIndex> {
         use InferTy::*;
         match ty {