Suggest considering casting fn item as fn pointer in more cases

compiler/rustc_trait_selection/src/errors.rs

@@ -1498,6 +1498,12 @@ pub struct FnConsiderCasting {
     pub casting: String,
 }
 
+#[derive(Subdiagnostic)]
+#[help(trait_selection_fn_consider_casting_both)]
+pub struct FnConsiderCastingBoth<'a> {
+    pub sig: Binder<'a, FnSig<'a>>,
+}
+
 #[derive(Subdiagnostic)]
 pub enum SuggestAccessingField<'a> {
     #[suggestion(