LibWeb+LibWebView+WebContent: Add APIs to manage an autoplay allowlist

The spec defines a Permissions Policy to control some browser behaviors
on a per-origin basis. Management of these permissions live in their own
spec: https://w3c.github.io/webappsec-permissions-policy/

This implements a somewhat ad-hoc Permissions Policy for autoplaying
media elements. We will need to implement the entire policy spec for
this to be more general.

Userland/Libraries/LibWeb/PermissionsPolicy/Decision.h

@@ -0,0 +1,16 @@
+/*
+ * Copyright (c) 2023, Tim Flynn <trflynn89@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+namespace Web::PermissionsPolicy {
+
+enum class Decision {
+    Enabled,
+    Disabled,
+};
+
+}