LibGUI: Add a GFontDatabase class that lets you enumerate fonts and more.

"More" in this case being also giving you the ability to load a font by name.
Use this as backend for Terminal's font menu. :^)

LibGUI/GFontDatabase.h

@@ -0,0 +1,21 @@
+#pragma once
+
+#include <AK/AKString.h>
+#include <AK/HashMap.h>
+#include <AK/Function.h>
+
+class Font;
+
+class GFontDatabase {
+public:
+    static GFontDatabase& the();
+
+    RetainPtr<Font> get_by_name(const String&);
+    void for_each_font(Function<void(const String&)>);
+
+private:
+    GFontDatabase();
+    ~GFontDatabase();
+
+    HashMap<String, String> m_name_to_path;
+};