LibGUI: Split HorizontalSlider to separate header

This patch splits HorizontalSlider to separate header so it can be used
as a component in .gml files with new GML compiler.

Userland/Applications/MouseSettings/MouseWidget.cpp

@@ -8,6 +8,7 @@
 
 #include <Applications/MouseSettings/MouseWidgetGML.h>
 #include <LibGUI/ConnectionToWindowServer.h>
+#include <LibGUI/HorizontalSlider.h>
 #include <LibGUI/ImageWidget.h>
 #include <LibGUI/Label.h>
 #include <LibGUI/Slider.h>

Userland/Applications/SoundPlayer/SoundPlayerWidget.h

@@ -13,6 +13,7 @@
 #include <AK/FixedArray.h>
 #include <AK/NonnullRefPtr.h>
 #include <LibAudio/ConnectionToServer.h>
+#include <LibGUI/HorizontalSlider.h>
 #include <LibGUI/Slider.h>
 #include <LibGUI/Splitter.h>
 #include <LibGUI/Widget.h>

Userland/Applications/VideoPlayer/VideoPlayerWidget.cpp

@@ -10,6 +10,7 @@
 #include <LibGUI/Action.h>
 #include <LibGUI/BoxLayout.h>
 #include <LibGUI/FilePicker.h>
+#include <LibGUI/HorizontalSlider.h>
 #include <LibGUI/ImageWidget.h>
 #include <LibGUI/Label.h>
 #include <LibGUI/MessageBox.h>

Userland/Demos/WidgetGallery/GalleryWidget.h

@@ -8,6 +8,7 @@
 
 #include <LibGUI/ColorInput.h>
 #include <LibGUI/ComboBox.h>
+#include <LibGUI/HorizontalSlider.h>
 #include <LibGUI/ImageWidget.h>
 #include <LibGUI/MessageBox.h>
 #include <LibGUI/OpacitySlider.h>

Userland/Libraries/LibGUI/HorizontalSlider.h

@@ -0,0 +1,27 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2022, the SerenityOS developers.
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibGUI/Slider.h>
+
+namespace GUI {
+
+class HorizontalSlider final : public Slider {
+    C_OBJECT(HorizontalSlider);
+
+public:
+    virtual ~HorizontalSlider() override = default;
+
+private:
+    HorizontalSlider()
+        : Slider(Orientation::Horizontal)
+    {
+    }
+};
+
+}

Userland/Libraries/LibGUI/Slider.cpp

@@ -6,6 +6,7 @@
  */
 
 #include <AK/StdLibExtras.h>
+#include <LibGUI/HorizontalSlider.h>
 #include <LibGUI/Painter.h>
 #include <LibGUI/Slider.h>
 #include <LibGfx/Palette.h>

Userland/Libraries/LibGUI/Slider.h

@@ -82,17 +82,4 @@ private:
     }
 };
 
-class HorizontalSlider final : public Slider {
-    C_OBJECT(HorizontalSlider);
-
-public:
-    virtual ~HorizontalSlider() override = default;
-
-private:
-    HorizontalSlider()
-        : Slider(Orientation::Horizontal)
-    {
-    }
-};
-
 }