HackStudio: Make the widget toolbar buttons checkable and exclusive

This way you can see which tool you've currently got selected, and it
doesn't let you select more than one at once.

DevTools/HackStudio/main.cpp

@@ -1,6 +1,5 @@
 #include "CppLexer.h"
 #include "CursorTool.h"
-#include "WidgetTool.h"
 #include "Editor.h"
 #include "EditorWrapper.h"
 #include "FindInFilesWidget.h"
@@ -9,9 +8,11 @@
 #include "Locator.h"
 #include "Project.h"
 #include "TerminalWrapper.h"
+#include "WidgetTool.h"
 #include <LibCore/CFile.h>
 #include <LibGUI/GAboutDialog.h>
 #include <LibGUI/GAction.h>
+#include <LibGUI/GActionGroup.h>
 #include <LibGUI/GApplication.h>
 #include <LibGUI/GBoxLayout.h>
 #include <LibGUI/GButton.h>
@@ -130,9 +131,17 @@ int main(int argc, char** argv)
  auto form_widgets_toolbar = GToolBar::construct(Orientation::Vertical, 26, g_form_inner_container);
  form_widgets_toolbar->set_preferred_size(38, 0);
 
- form_widgets_toolbar->add_action(GAction::create("Cursor", GraphicsBitmap::load_from_file("/res/icons/widgets/Cursor.png"), [&](auto&) {
+ GActionGroup tool_actions;
+ tool_actions.set_exclusive(true);
+
+ auto cursor_tool_action = GAction::create("Cursor", GraphicsBitmap::load_from_file("/res/icons/widgets/Cursor.png"), [&](auto&) {
  g_form_editor_widget->set_tool(make<CursorTool>(*g_form_editor_widget));
- }));
+ });
+ cursor_tool_action->set_checkable(true);
+ cursor_tool_action->set_checked(true);
+ tool_actions.add_action(cursor_tool_action);
+
+ form_widgets_toolbar->add_action(cursor_tool_action);
 
  GWidgetClassRegistration::for_each([&](const GWidgetClassRegistration& reg) {
  auto icon_path = String::format("/res/icons/widgets/%s.png", reg.class_name().characters());
@@ -141,6 +150,9 @@ int main(int argc, char** argv)
  auto widget = reg.construct(&g_form_editor_widget->form_widget());
  widget->set_relative_rect(30, 30, 30, 30);
  });
+ action->set_checkable(true);
+ action->set_checked(false);
+ tool_actions.add_action(action);
  form_widgets_toolbar->add_action(move(action));
  });