DisplaySettings: Link to cursor themes from "Themes" tab

This removes a few clicks to access the mouse settings and puts
all theming actions in one place.

Userland/Applications/DisplaySettings/ThemesSettings.gml

@@ -4,6 +4,13 @@
         margins: [8]
     }
 
+    @GUI::GroupBox {
+        layout: @GUI::VerticalBoxLayout {
+            margins: [14, 14, 4]
+        }
+        title: "Window Theme"
+        fixed_height: 294
+
         @GUI::Frame {
             layout: @GUI::HorizontalBoxLayout {}
             name: "preview_frame"
@@ -30,3 +37,22 @@
             }
         }
     }
+
+    @GUI::GroupBox {
+        layout: @GUI::VerticalBoxLayout {
+            margins: [14, 14, 4]
+        }
+        title: "Cursor Theme"
+        shrink_to_fit: true
+
+        @GUI::Button {
+            name: "cursor_themes_button"
+            text: "Change in Mouse Settings..."
+            fixed_width: 200
+        }
+
+        @GUI::Widget {
+            fixed_height: 10
+        }
+    }
+}

Userland/Applications/DisplaySettings/ThemesSettingsWidget.cpp

@@ -11,6 +11,7 @@
 #include <LibCore/DirIterator.h>
 #include <LibGUI/ConnectionToWindowServer.h>
 #include <LibGUI/ItemListModel.h>
+#include <LibGUI/Process.h>
 
 namespace DisplaySettings {
 
@@ -36,7 +37,6 @@ ThemesSettingsWidget::ThemesSettingsWidget(bool& background_settings_changed)
         }
     }
     VERIFY(m_selected_theme);
-
     m_theme_preview = find_descendant_of_type_named<GUI::Frame>("preview_frame")->add<ThemePreviewWidget>(palette());
     m_themes_combo = *find_descendant_of_type_named<GUI::ComboBox>("themes_combo");
     m_themes_combo->set_only_allow_values_from_model(true);
@@ -47,6 +47,13 @@ ThemesSettingsWidget::ThemesSettingsWidget(bool& background_settings_changed)
         set_modified(true);
     };
     m_themes_combo->set_selected_index(current_theme_index, GUI::AllowCallback::No);
+
+    auto mouse_settings_icon = Gfx::Bitmap::try_load_from_file("res/icons/16x16/app-mouse.png").release_value_but_fixme_should_propagate_errors();
+    m_cursor_themes_button = *find_descendant_of_type_named<GUI::Button>("cursor_themes_button");
+    m_cursor_themes_button->set_icon(mouse_settings_icon);
+    m_cursor_themes_button->on_click = [&](auto) {
+        GUI::Process::spawn_or_show_error(window(), "/bin/MouseSettings", Array { "-t", "cursor-theme" });
+    };
 }
 
 void ThemesSettingsWidget::apply_settings()

Userland/Applications/DisplaySettings/ThemesSettingsWidget.h

@@ -28,9 +28,10 @@ private:
 
     RefPtr<GUI::ComboBox> m_themes_combo;
     RefPtr<ThemePreviewWidget> m_theme_preview;
-
     Gfx::SystemThemeMetaData const* m_selected_theme { nullptr };
 
+    RefPtr<GUI::Button> m_cursor_themes_button;
+
     bool& m_background_settings_changed;
 
     ThemesSettingsWidget(bool& background_settings_changed);

Userland/Applications/DisplaySettings/main.cpp

@@ -21,7 +21,7 @@
 
 ErrorOr<int> serenity_main(Main::Arguments arguments)
 {
-    TRY(Core::System::pledge("stdio thread recvfd sendfd rpath cpath wpath unix"));
+    TRY(Core::System::pledge("stdio thread recvfd sendfd rpath cpath wpath unix proc exec"));
 
     auto app = TRY(GUI::Application::try_create(arguments));
     Config::pledge_domain("WindowManager");