wrong_self_convention: Match SelfKind::No more restrictively

The `wrong_self_convention` lint uses a `SelfKind` type to decide
whether a method has the right kind of "self" for its name, or whether
the kind of "self" it has makes its name confusable for a method in
a common trait.  One possibility is `SelfKind::No`, which is supposed
to mean "No `self`".

Previously, SelfKind::No matched everything _except_ Self, including
references to Self.  This patch changes it to match Self, &Self, &mut
Self, Box<Self>, and so on.

For example, this kind of method was allowed before:

```
impl S {
    // Should trigger the lint, because
    // "methods called `is_*` usually take `self` by reference or no `self`"
    fn is_foo(&mut self) -> bool { todo!() }
}
```

But since SelfKind::No matched "&mut self", no lint was triggered
(see #8142).

With this patch, the code above now gives a lint as expected.

Fixes #8142

changelog: [`wrong_self_convention`] rejects `self` references in more cases

clippy_lints/src/methods/mod.rs

@@ -2535,11 +2535,17 @@ impl SelfKind {
             implements_trait(cx, ty, trait_def_id, &[parent_ty.into()])
         }
 
+        fn matches_none<'a>(cx: &LateContext<'a>, parent_ty: Ty<'a>, ty: Ty<'a>) -> bool {
+            !matches_value(cx, parent_ty, ty)
+                && !matches_ref(cx, hir::Mutability::Not, parent_ty, ty)
+                && !matches_ref(cx, hir::Mutability::Mut, parent_ty, ty)
+        }
+
         match self {
             Self::Value => matches_value(cx, parent_ty, ty),
             Self::Ref => matches_ref(cx, hir::Mutability::Not, parent_ty, ty) || ty == parent_ty && is_copy(cx, ty),
             Self::RefMut => matches_ref(cx, hir::Mutability::Mut, parent_ty, ty),
-            Self::No => ty != parent_ty,
+            Self::No => matches_none(cx, parent_ty, ty),
         }
     }