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/Slide.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
  */
@@ -9,19 +10,18 @@
 #include "SlideObject.h"
 #include <AK/DeprecatedString.h>
 #include <AK/Forward.h>
-#include <AK/NonnullOwnPtrVector.h>
-#include <LibGfx/Forward.h>
+#include <AK/NonnullRefPtrVector.h>
 
 // A single slide of a presentation.
 class Slide final {
 public:
-    static ErrorOr<Slide> parse_slide(JsonObject const& slide_json, NonnullRefPtr<GUI::Window> window);
+    static ErrorOr<Slide> parse_slide(JsonObject const& slide_json);
 
     // FIXME: shouldn't be hard-coded to 1.
     unsigned frame_count() const { return 1; }
     StringView title() const { return m_title; }
 
-    void paint(Gfx::Painter&, unsigned current_frame, Gfx::FloatSize display_scale) const;
+    ErrorOr<HTMLElement> render(Presentation const&) const;
 
 private:
     Slide(NonnullRefPtrVector<SlideObject> slide_objects, DeprecatedString title);