Auto merge of #13225 - lowr:fix/hir-proj-normalization, r=Veykril

fixup: remove unnecessary `Option`

Fixup for #13223, two things:

- `normalize_projection_query()` (and consequently `HirDatabase::normalize_projection()`) never returns `None` (well, it used to when I first wrote it...), so just return `Ty` instead of `Option<Ty>`
- When chalk cannot normalize projection uniquely, `normalize_trait_assoc_type()` used to return `None` before #13223, but not anymore because of the first point. I restored the behavior so its callers work as before.

crates/hir/src/lib.rs

@@ -2892,7 +2892,12 @@ impl Type {
             })
             .build();
 
-        db.normalize_projection(projection, self.env.clone()).map(|ty| self.derived(ty))
+        let ty = db.normalize_projection(projection, self.env.clone());
+        if ty.is_unknown() {
+            None
+        } else {
+            Some(self.derived(ty))
+        }
     }
 
     pub fn is_copy(&self, db: &dyn HirDatabase) -> bool {