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.cpp

@@ -0,0 +1,17 @@
+/*
+ * Copyright (c) 2022, Sam Atkins <atkinssj@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibWeb/CSS/FontFace.h>
+
+namespace Web::CSS {
+
+FontFace::FontFace(FlyString font_family, Vector<Source> sources)
+    : m_font_family(move(font_family))
+    , m_sources(move(sources))
+{
+}
+
+}