implement most of feature(more_qualified_paths)

This handles
```rust
let <T as Trait>::Assoc { a } = <T as Trait>::Assoc { a: 0 };
let (<E as Trait>::Assoc::ES { a } | <E as Trait>::Assoc::ET(a))
    = <E as Trait>::Assoc::ES { a: 0 };
```

Author: WaffleLapkin

crates/hir-ty/src/infer.rs

@@ -1646,10 +1646,24 @@ impl<'db> InferenceContext<'db> {
                 let ty = self.insert_type_vars(ty.substitute(Interner, &substs));
                 forbid_unresolved_segments((ty, Some(var.into())), unresolved)
             }
-            TypeNs::SelfType(impl_id) => {
-                let generics = crate::generics::generics(self.db, impl_id.into());
-                let substs = generics.placeholder_subst(self.db);
-                let mut ty = self.db.impl_self_ty(impl_id).substitute(Interner, &substs);
+            TypeNs::SelfType(_) | TypeNs::TraitId(_) => {
+                let mut ty = match resolution {
+                    TypeNs::TraitId(_) => {
+                        let args = path.generic_args().unwrap()[0].as_ref().unwrap();
+                        assert!(args.has_self_type);
+                        let hir_def::expr_store::path::GenericArg::Type(type_idx) = args.args[0]
+                        else {
+                            panic!()
+                        };
+                        path_ctx.ty_ctx().lower_ty(type_idx)
+                    }
+                    TypeNs::SelfType(impl_id) => {
+                        let generics = crate::generics::generics(self.db, impl_id.into());
+                        let substs = generics.placeholder_subst(self.db);
+                        self.db.impl_self_ty(impl_id).substitute(Interner, &substs)
+                    }
+                    _ => unreachable!(),
+                };
 
                 let Some(remaining_idx) = unresolved else {
                     drop(ctx);
@@ -1741,7 +1755,6 @@ impl<'db> InferenceContext<'db> {
             }
             TypeNs::AdtId(AdtId::EnumId(_))
             | TypeNs::BuiltinType(_)
-            | TypeNs::TraitId(_)
             | TypeNs::TraitAliasId(_)
             | TypeNs::ModuleId(_) => {
                 // FIXME diagnostic