LibWeb+WebContent: Move Serenity EventLoop and Font plugins into LibWeb

These are exactly what's wanted by headless-browser too, so this saves
us some duplication. LibWeb already links LibCore so it should not
cause any issues for Ladybird.

Userland/Libraries/LibWeb/Platform/FontPluginSerenity.cpp

@@ -0,0 +1,54 @@
+/*
+ * Copyright (c) 2022, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include "FontPluginSerenity.h"
+#include <AK/String.h>
+#include <LibGfx/Font/FontDatabase.h>
+
+namespace Web::Platform {
+
+FontPluginSerenity::FontPluginSerenity()
+{
+}
+
+FontPluginSerenity::~FontPluginSerenity() = default;
+
+Gfx::Font& FontPluginSerenity::default_font()
+{
+    return Gfx::FontDatabase::default_font();
+}
+
+Gfx::Font& FontPluginSerenity::default_fixed_width_font()
+{
+    return Gfx::FontDatabase::default_fixed_width_font();
+}
+
+String FontPluginSerenity::generic_font_name(GenericFont generic_font)
+{
+    // FIXME: Replace hard-coded font names with a relevant call to FontDatabase.
+    // Currently, we cannot request the default font's name, or request it at a specific size and weight.
+    // So, hard-coded font names it is.
+    switch (generic_font) {
+    case GenericFont::SansSerif:
+    case GenericFont::UiSansSerif:
+    case GenericFont::Cursive:
+    case GenericFont::UiRounded:
+        return "Katica";
+    case GenericFont::Monospace:
+    case GenericFont::UiMonospace:
+        return "Csilla";
+    case GenericFont::Serif:
+    case GenericFont::UiSerif:
+        return "Roman";
+    case GenericFont::Fantasy:
+        return "Comic Book";
+    case GenericFont::__Count:
+        VERIFY_NOT_REACHED();
+    }
+    VERIFY_NOT_REACHED();
+}
+
+}