LibGUI: Add and use Window::center_on_screen()

Various applications were using the same slightly verbose code to center
themselves on the screen/desktop:

Gfx::IntRect window_rect { 0, 0, width, height };
window_rect.center_within(GUI::Desktop::the().rect());
window->set_rect(window_rect);

Which now becomes:

window->resize(width, height);
window->center_on_screen();

Applications/Welcome/main.cpp

@@ -35,7 +35,6 @@
 #include <LibGUI/Application.h>
 #include <LibGUI/BoxLayout.h>
 #include <LibGUI/Button.h>
-#include <LibGUI/Desktop.h>
 #include <LibGUI/ImageWidget.h>
 #include <LibGUI/Label.h>
 #include <LibGUI/MessageBox.h>
@@ -156,10 +155,8 @@ int main(int argc, char** argv)
 
     auto window = GUI::Window::construct();
     window->set_title("Welcome");
-    Gfx::IntRect window_rect { 0, 0, 640, 360 };
-    window_rect.center_within(GUI::Desktop::the().rect());
-    window->set_resizable(true);
-    window->set_rect(window_rect);
+    window->resize(640, 360);
+    window->center_on_screen();
 
     auto& background = window->set_main_widget<BackgroundWidget>();
     background.set_fill_with_background_color(false);

DevTools/Profiler/main.cpp

@@ -137,9 +137,8 @@ static bool prompt_to_stop_profiling()
     auto window = GUI::Window::construct();
     window->set_title("Profiling");
     window->set_icon(Gfx::Bitmap::load_from_file("/res/icons/16x16/app-profiler.png"));
-    Gfx::IntRect window_rect { 0, 0, 320, 200 };
-    window_rect.center_within(GUI::Desktop::the().rect());
-    window->set_rect(window_rect);
+    window->resize(320, 200);
+    window->center_on_screen();
     auto& widget = window->set_main_widget<GUI::Widget>();
     widget.set_fill_with_background_color(true);
     widget.set_layout<GUI::VerticalBoxLayout>();

Libraries/LibGUI/ProcessChooser.cpp

@@ -26,7 +26,6 @@
 
 #include <LibGUI/BoxLayout.h>
 #include <LibGUI/Button.h>
-#include <LibGUI/Desktop.h>
 #include <LibGUI/MessageBox.h>
 #include <LibGUI/ProcessChooser.h>
 #include <LibGUI/RunningProcessesModel.h>
@@ -48,9 +47,8 @@ ProcessChooser::ProcessChooser(const StringView& window_title, const StringView&
     else if (parent_window)
         set_icon(parent_window->icon());
 
-    Gfx::IntRect window_rect { 0, 0, 300, 340 };
-    window_rect.center_within(GUI::Desktop::the().rect());
-    set_rect(window_rect);
+    resize(300, 340);
+    center_on_screen();
 
     auto& widget = set_main_widget<GUI::Widget>();
     widget.set_fill_with_background_color(true);

Libraries/LibGUI/Window.cpp

@@ -32,6 +32,7 @@
 #include <LibCore/MimeData.h>
 #include <LibGUI/Action.h>
 #include <LibGUI/Application.h>
+#include <LibGUI/Desktop.h>
 #include <LibGUI/Event.h>
 #include <LibGUI/Painter.h>
 #include <LibGUI/Widget.h>
@@ -212,6 +213,13 @@ void Window::set_rect(const Gfx::IntRect& a_rect)
         m_main_widget->resize(window_rect.size());
 }
 
+void Window::center_on_screen()
+{
+    auto window_rect = rect();
+    window_rect.center_within(Desktop::the().rect());
+    set_rect(window_rect);
+}
+
 void Window::set_window_type(WindowType window_type)
 {
     m_window_type = window_type;

Libraries/LibGUI/Window.h

@@ -123,6 +123,8 @@ public:
     void resize(int width, int height) { resize({ width, height }); }
     void resize(const Gfx::IntSize& size) { set_rect({ position(), size }); }
 
+    void center_on_screen();
+
     virtual void event(Core::Event&) override;
 
     bool is_visible() const;

Services/SystemMenu/ShutdownDialog.cpp

@@ -29,7 +29,6 @@
 #include <AK/Vector.h>
 #include <LibGUI/BoxLayout.h>
 #include <LibGUI/Button.h>
-#include <LibGUI/Desktop.h>
 #include <LibGUI/Label.h>
 #include <LibGUI/RadioButton.h>
 #include <LibGUI/Widget.h>
@@ -62,9 +61,8 @@ Vector<char const*> ShutdownDialog::show()
 ShutdownDialog::ShutdownDialog()
     : Dialog(nullptr)
 {
-    Gfx::IntRect rect({ 0, 0, 180, 180 + ((static_cast<int>(options.size()) - 3) * 16) });
-    rect.center_within(GUI::Desktop::the().rect());
-    set_rect(rect);
+    resize(180, 180 + ((static_cast<int>(options.size()) - 3) * 16));
+    center_on_screen();
     set_resizable(false);
     set_title("SerenityOS");
     set_icon(Gfx::Bitmap::load_from_file("/res/icons/16x16/power.png"));