LibWeb: Introduce Content Security Policy policies and directives

These form the basis of Content Security Policy. A policy is a
collection of directives that are parsed from either the
Content-Security-Policy(-Report-Only) HTTP header, or the `<meta>`
element.

The directives are what restrict the operations can be performed in the
current global execution context. For example, "frame-ancestors: none"
tells us to prevent the page from being loaded in an embedded context,
such as `<iframe>`.

You can see it a bit like OpenBSD's pledge() functionality, but for the
web platform: https://man.openbsd.org/pledge.2

Libraries/LibWeb/ContentSecurityPolicy/Directives/Directive.cpp

@@ -0,0 +1,35 @@
+/*
+ * Copyright (c) 2025, Luke Wilde <luke@ladybird.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibJS/Runtime/Realm.h>
+#include <LibWeb/ContentSecurityPolicy/Directives/Directive.h>
+#include <LibWeb/ContentSecurityPolicy/Directives/DirectiveFactory.h>
+#include <LibWeb/ContentSecurityPolicy/Directives/SerializedDirective.h>
+
+namespace Web::ContentSecurityPolicy::Directives {
+
+GC_DEFINE_ALLOCATOR(Directive);
+
+Directive::Directive(String name, Vector<String> value)
+    : m_name(move(name))
+    , m_value(move(value))
+{
+}
+
+GC::Ref<Directive> Directive::clone(JS::Realm& realm) const
+{
+    return create_directive(realm, m_name, m_value);
+}
+
+SerializedDirective Directive::serialize() const
+{
+    return SerializedDirective {
+        .name = m_name,
+        .value = m_value,
+    };
+}
+
+}