Add test for reexported hidden item with --document-hidden-items

Author: GuillaumeGomez

tests/rustdoc-json/reexport/reexport_of_hidden.rs

@@ -0,0 +1,10 @@
+// compile-flags: --document-hidden-items
+
+// @has "$.index[*].inner[?(@.import.name=='UsedHidden')]"
+// @has "$.index[*][?(@.name=='Hidden')]"
+pub mod submodule {
+    #[doc(hidden)]
+    pub struct Hidden {}
+}
+
+pub use submodule::Hidden as UsedHidden;