Auto merge of rust-lang#15288 - alibektas:15143, r=lnicola

Handle TyAlias in projected_ty

First of all I still have no idea how MIR works but rust-lang#15143 has been an issue that constantly made RA crash so I have been looking for a way to make RA stop panicking. I have zero claims that what I want to merge has any sense or is correct 😄  but there isn't any more panicking. Even if it is wrong may this be at least a step towards resolving this issue.
As is customary this PR fixes rust-lang#15143

Author: bors

crates/hir-ty/src/mir.rs

@@ -151,6 +151,7 @@ impl<V, T> ProjectionElem<V, T> {
                 TyKind::Adt(_, subst) => {
                     db.field_types(f.parent)[f.local_id].clone().substitute(Interner, subst)
                 }
+                TyKind::Alias(inner) => inner.clone().intern(Interner),
                 _ => {
                     never!("Only adt has field");
                     return TyKind::Error.intern(Interner);
@@ -167,6 +168,7 @@ impl<V, T> ProjectionElem<V, T> {
                         TyKind::Error.intern(Interner)
                     }),
                 TyKind::Closure(id, subst) => closure_field(*id, subst, *f),
+                TyKind::Alias(inner) => inner.clone().intern(Interner),
                 _ => {
                     never!("Only tuple or closure has tuple or closure field");
                     return TyKind::Error.intern(Interner);