LibWeb: Add referrer policy to Fetch::Infrastructure::Request

The enum is in its own directory and namespace as there's a standalone
spec for it, that will later also house AOs.

- https://w3c.github.io/webappsec-referrer-policy/
- https://www.w3.org/TR/referrer-policy/

Userland/Libraries/LibWeb/ReferrerPolicy/ReferrerPolicy.h

@@ -0,0 +1,23 @@
+/*
+ * Copyright (c) 2022, Linus Groh <linusg@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+namespace Web::ReferrerPolicy {
+
+// https://w3c.github.io/webappsec-referrer-policy/#enumdef-referrerpolicy
+enum class ReferrerPolicy {
+    NoReferrer,
+    NoReferrerWhenDowngrade,
+    SameOrigin,
+    Origin,
+    StrictOrigin,
+    OriginWhenCrossOrigin,
+    StrictOriginWhenCrossOrigin,
+    UnsafeURL,
+};
+
+}