Rollup merge of rust-lang#144838 - Kivooeo:doc-subtype, r=notriddle

Fix outdated doc comment

This updates the documentation comment for `Type::is_doc_subtype_of` to more accurately describe its purpose as a subtyping check, rather than equality

fixes rust-lang#138572

r? `````````@tgross35`````````

Author: jhpratt

src/librustdoc/clean/types.rs

@@ -1552,10 +1552,10 @@ impl Type {
         matches!(self, Type::Path { path: Path { res: Res::Def(DefKind::TyAlias, _), .. } })
     }
 
-    /// Check if two types are "the same" for documentation purposes.
+    /// Check if this type is a subtype of another type for documentation purposes.
     ///
     /// This is different from `Eq`, because it knows that things like
-    /// `Placeholder` are possible matches for everything.
+    /// `Infer` and generics have special subtyping rules.
     ///
     /// This relation is not commutative when generics are involved:
     ///
@@ -1566,8 +1566,8 @@ impl Type {
     /// let cache = Cache::new(false);
     /// let generic = Type::Generic(rustc_span::symbol::sym::Any);
     /// let unit = Type::Primitive(PrimitiveType::Unit);
-    /// assert!(!generic.is_same(&unit, &cache));
-    /// assert!(unit.is_same(&generic, &cache));
+    /// assert!(!generic.is_doc_subtype_of(&unit, &cache));
+    /// assert!(unit.is_doc_subtype_of(&generic, &cache));
     /// ```
     ///
     /// An owned type is also the same as its borrowed variants (this is commutative),