Modal window below main window

If we click in the main window when a modal window is running (e.g. Canvas Size), the main attachment window is going to the top, but still we cannot click it.

https://github.com/aseprite/Attachment-System/assets/39654/fc0b668b-f62c-4905-bad1-b75a6f6d2bd9

This requires some low level API in the laf side to avoid sending other windows to the top when there is one modal window running.

Reproduce the issue using a modal window such as Canvas Size, then inspect the laf-side window activation behavior described in the report. Trace what happens when the main attachment window is clicked while the modal is open. Done means the main window no longer comes to the top or accepts focus while a modal window is running.

Written by the indexing model from the issue text.