Rollup merge of #111486 - fmease:pp-inh-proj, r=petrochenkov

Pretty-print inherent projections correctly

Previously, we were trying to pretty-print inherent projections with `Printer::print_def_path` which is incorrect since
it expects the substitutions to be of a certain format (parents substs followed by own substs) which doesn't hold for
inherent projections (self type subst followed by own substs).
Now we print inherent projections manually.

Fixes #111390.
Fixes #111397.

Lacking tests! Is there a test suite / compiletest flags for the pretty-printer? In most if not all cases,
inherent projections are normalized away before they get the chance to appear in diagnostics.

If I were to create regression tests for linked issues, they would need to be `mir-opt` tests to exercise
`-Zdump-mir=all` (right?) which doesn't feel quite adequate to me.

`@rustbot` label F-inherent_associated_types

compiler/rustc_const_eval/src/util/type_name.rs

@@ -58,11 +58,12 @@ impl<'tcx> Printer<'tcx> for AbsolutePathPrinter<'tcx> {
             // Types with identity (print the module path).
             ty::Adt(ty::AdtDef(Interned(&ty::AdtDefData { did: def_id, .. }, _)), substs)
             | ty::FnDef(def_id, substs)
-            | ty::Alias(_, ty::AliasTy { def_id, substs, .. })
+            | ty::Alias(ty::Projection | ty::Opaque, ty::AliasTy { def_id, substs, .. })
             | ty::Closure(def_id, substs)
             | ty::Generator(def_id, substs, _) => self.print_def_path(def_id, substs),
             ty::Foreign(def_id) => self.print_def_path(def_id, &[]),
 
+            ty::Alias(ty::Inherent, _) => bug!("type_name: unexpected inherent projection"),
             ty::GeneratorWitness(_) => bug!("type_name: unexpected `GeneratorWitness`"),
             ty::GeneratorWitnessMIR(..) => bug!("type_name: unexpected `GeneratorWitnessMIR`"),
         }