Presenter: Rearchitect on top of LibWeb

This patch replaces the bespoke rendering engine in Presenter with a
simple pipeline that turns presentations into single-page HTML files.
The HTML is then loaded into an OutOfProcessWebView.

This achieves a number of things, most importantly:
- Access to all the CSS features supported by LibWeb
- Sandboxed, multi-process rendering

The code could be simplified a lot further, but I wanted to get the new
architecture in place without changing anything about the file format.

Userland/Applications/Presenter/PresenterWidget.h

@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2022, kleines Filmröllchen <filmroellchen@serenityos.org>
+ * Copyright (c) 2023, Andreas Kling <kling@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -11,6 +12,7 @@
 #include <LibGUI/Event.h>
 #include <LibGUI/UIDimensions.h>
 #include <LibGUI/Widget.h>
+#include <LibWebView/OutOfProcessWebView.h>
 
 // Title, Author
 constexpr StringView const title_template = "{} ({}) — Presenter"sv;
@@ -29,11 +31,17 @@ public:
 
 protected:
     virtual void paint_event(GUI::PaintEvent&) override;
+    virtual void second_paint_event(GUI::PaintEvent&) override;
     virtual void keydown_event(GUI::KeyEvent&) override;
     virtual void drag_enter_event(GUI::DragEvent&) override;
     virtual void drop_event(GUI::DropEvent&) override;
+    virtual void resize_event(GUI::ResizeEvent&) override;
 
 private:
+    void update_web_view();
+
+    RefPtr<WebView::OutOfProcessWebView> m_web_view;
+
     OwnPtr<Presentation> m_current_presentation;
     RefPtr<GUI::Action> m_next_slide_action;
     RefPtr<GUI::Action> m_previous_slide_action;