rustdoc-json: Add test for #[automatically_derived] attribute

Author: aDotInTheVoid

tests/rustdoc-json/attrs/automatically_derived.rs

@@ -0,0 +1,13 @@
+#[derive(Default)]
+pub struct Derive;
+
+pub struct Manual;
+
+impl Default for Manual {
+    fn default() -> Self {
+        Self
+    }
+}
+
+//@ is '$.index[?(@.inner.impl.for.resolved_path.path == "Derive" && @.inner.impl.trait.path == "Default")].attrs' '["#[automatically_derived]"]'
+//@ is '$.index[?(@.inner.impl.for.resolved_path.path == "Manual" && @.inner.impl.trait.path == "Default")].attrs' '[]'