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.cpp

@@ -0,0 +1,50 @@
+#include <LibGUI/GFontDatabase.h>
+#include <SharedGraphics/Font.h>
+#include <dirent.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+static GFontDatabase* s_the;
+
+GFontDatabase& GFontDatabase::the()
+{
+    if (!s_the)
+        s_the = new GFontDatabase;
+    return *s_the;
+}
+
+GFontDatabase::GFontDatabase()
+{
+    DIR* dirp = opendir("/res/fonts");
+    if (!dirp) {
+        perror("opendir");
+        exit(1);
+    }
+    while (auto* de = readdir(dirp)) {
+        if (de->d_name[0] == '.')
+            continue;
+        auto path = String::format("/res/fonts/%s", de->d_name);
+        if (auto font = Font::load_from_file(path))
+            m_name_to_path.set(font->name(), path);
+    }
+    closedir(dirp);
+}
+
+GFontDatabase::~GFontDatabase()
+{
+}
+
+void GFontDatabase::for_each_font(Function<void(const String&)> callback)
+{
+    for (auto& it : m_name_to_path) {
+        callback(it.key);
+    }
+}
+
+RetainPtr<Font> GFontDatabase::get_by_name(const String& name)
+{
+    auto it = m_name_to_path.find(name);
+    if (it == m_name_to_path.end())
+        return nullptr;
+    return Font::load_from_file((*it).value);
+}