Fix preloading a zip in the web editor

[paulsinnett]

When the versions went from 3 to 4 the MainLoop no longer responds to the files_dropped signal. This change sends the files_dropped signal to the root window and causes it to open the import dialog box.

• Bugsquad edit, fixes: Web Editor Preload doesn't automatically prompt to create folder #85855

[akien-mga]

Amended the commit message to be clearer than "fix" (and squash the commits). Please keep in mind to write clear commit messages for future PRs, see https://github.com/godotengine/godot/blob/master/CONTRIBUTING.md#format-your-commit-messages-with-readability-in-mind

[akien-mga]

Thanks! And congrats for your first merged Godot contribution 🎉

[akien-mga]

Seems like I introduced a bug when rebasing, I changed the include from scene/main/window.h to scene/main/scene_tree.h as this is what's being used, but it seems scene_tree.h only forward declares Window and relies on window.h being included when using it (which IMO is a bug). I'll fix it up.

platform/web/web_main.cpp:134:41: error: member access into incomplete type 'Window'
  134 |                 SceneTree::get_singleton()->get_root()->emit_signal(SNAME("files_dropped"), ps);
      |                                                       ^
./scene/main/scene_tree.h:44:7: note: forward declaration of 'Window'
   44 | class Window;
      |       ^

[akien-mga]

Fixed up with ce16818. We should look into actually including window.h in scene_tree.h later on, but there's an #undef Window there so I suspect it might be a situation of circular deps.