VideoPlayer: Start fleshing out the user interface

This adds player widget with working play/pause controls, a seek bar
which currently only displays the current playback position, and a
button to cycle between the scaling modes.

The player uses the new PlaybackManager class to handle demuxing,
decoding, and frame presentation timing.

Currently, the volume control is non-functional.

Userland/Applications/VideoPlayer/VideoFrameWidget.h

@@ -0,0 +1,72 @@
+/*
+ * Copyright (c) 2022, Gregory Bertilson <zaggy1024@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/StringView.h>
+#include <LibGUI/Event.h>
+#include <LibGUI/Frame.h>
+
+namespace VideoPlayer {
+
+enum class VideoSizingMode : u8 {
+    Fit,
+    Fill,
+    Stretch,
+    FullSize,
+    Sentinel
+};
+
+class VideoFrameWidget : public GUI::Frame {
+    C_OBJECT(VideoFrameWidget)
+public:
+    virtual ~VideoFrameWidget() override = default;
+
+    void set_bitmap(Gfx::Bitmap const*);
+    Gfx::Bitmap* bitmap() { return m_bitmap.ptr(); }
+    Gfx::Bitmap const* bitmap() const { return m_bitmap.ptr(); }
+
+    void set_sizing_mode(VideoSizingMode value) { m_sizing_mode = value; }
+    VideoSizingMode sizing_mode() const { return m_sizing_mode; }
+
+    void set_auto_resize(bool value);
+    bool auto_resize() const { return m_auto_resize; }
+
+    Function<void()> on_click;
+
+protected:
+    explicit VideoFrameWidget();
+
+    virtual void mousedown_event(GUI::MouseEvent&) override;
+    virtual void paint_event(GUI::PaintEvent&) override;
+
+private:
+    RefPtr<Gfx::Bitmap> m_bitmap;
+    VideoSizingMode m_sizing_mode { VideoSizingMode::Fit };
+    bool m_auto_resize { false };
+};
+
+constexpr StringView video_sizing_mode_name(VideoSizingMode mode)
+{
+    switch (mode) {
+    case VideoSizingMode::Fit:
+        return "Fit"sv;
+        break;
+    case VideoSizingMode::Fill:
+        return "Fill"sv;
+        break;
+    case VideoSizingMode::Stretch:
+        return "Stretch"sv;
+        break;
+    case VideoSizingMode::FullSize:
+        return "Full size"sv;
+        break;
+    default:
+        VERIFY_NOT_REACHED();
+    }
+}
+
+}