LibWeb: Implement initial CSSFontFaceRule and FontFace classes

For now, this is the bare minimum that's needed: font-family and src.

Userland/Libraries/LibWeb/CSS/FontFace.h

@@ -0,0 +1,32 @@
+/*
+ * Copyright (c) 2022, Sam Atkins <atkinssj@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/FlyString.h>
+#include <AK/URL.h>
+
+namespace Web::CSS {
+
+class FontFace {
+public:
+    struct Source {
+        AK::URL url;
+    };
+
+    FontFace(FlyString font_family, Vector<Source> sources);
+    ~FontFace() = default;
+
+    FlyString font_family() const { return m_font_family; }
+    Vector<Source> const& sources() const { return m_sources; }
+    // FIXME: font-style, font-weight, font-stretch, unicode-range, font-feature-settings
+
+private:
+    FlyString m_font_family;
+    Vector<Source> m_sources;
+};
+
+}