Tweak the default project icon

This only affects newly created projects.

- Use a 128×128 resolution to make the icon look crisp on hiDPI displays.
- Darken the icon's outside area and remove the border, as the
  contrast rate between the icon and its background is now sufficient.

This different design also allows distinguishing projects that
were made with Godot 3.x from projects made with Godot 4.0.

editor/project_manager.cpp

@@ -1178,6 +1178,12 @@ void ProjectList::load_project_icon(int p_index) {
 		icon = default_icon;
 	}
 
+	// The default project icon is 128×128 to look crisp on hiDPI displays,
+	// but we want the actual displayed size to be 64×64 on loDPI displays.
+	item.control->icon->set_ignore_texture_size(true);
+	item.control->icon->set_custom_minimum_size(Size2(64, 64) * EDSCALE);
+	item.control->icon->set_stretch_mode(TextureRect::STRETCH_KEEP_ASPECT_CENTERED);
+
 	item.control->icon->set_texture(icon);
 	item.control->icon_needs_reload = false;
 }