HackStudio: Make "Open project" action open in the current project path

Prior this change, the action opened a File Picker
in user home directory.

Changing the startup path to a project path might make correcting
the path or switching between different projects a bit faster,
as you don't have to go through the subdirectories all over again.
It's also the path that's showed in the project tree view.

Userland/DevTools/HackStudio/HackStudioWidget.cpp

@@ -587,7 +587,7 @@ NonnullRefPtr<GUI::Action> HackStudioWidget::create_remove_current_editor_action
 NonnullRefPtr<GUI::Action> HackStudioWidget::create_open_action()
 {
     return GUI::Action::create("&Open Project...", { Mod_Ctrl | Mod_Shift, Key_O }, Gfx::Bitmap::try_load_from_file("/res/icons/16x16/open.png"), [this](auto&) {
-        auto open_path = GUI::FilePicker::get_open_filepath(window(), "Open project", Core::StandardPaths::home_directory(), true);
+        auto open_path = GUI::FilePicker::get_open_filepath(window(), "Open project", m_project->root_path(), true);
         if (!open_path.has_value())
             return;
         open_project(open_path.value());