Rollup merge of #128721 - Brezak:pointee-in-strange-places, r=pnkfelix

Don't allow the `#[pointee]` attribute where it doesn't belong

Error if the `#[pointee]` attribute is applied to anything but generic type parameters.

Closes #128485
Related to #123430

compiler/rustc_builtin_macros/src/errors.rs

@@ -940,3 +940,10 @@ pub(crate) struct NakedFunctionTestingAttribute {
     #[label]
     pub testing_span: Span,
 }
+
+#[derive(Diagnostic)]
+#[diag(builtin_macros_non_generic_pointee)]
+pub(crate) struct NonGenericPointee {
+    #[primary_span]
+    pub span: Span,
+}