macos parent for sync FileDialog

[m11m]

I don't claim to know what I am doing, but here is something that worked for me. :)

Note: It does not result in the "sheet" behavior, but it does result in the "child window" behavior.

[m11m]

re: #53

[PolyMeilex]

Looks promising, does it produce child always on top of parent behavior?

[m11m]

I observe it working similarly to how it works without setting the child, except that when you move the parent window, the child moves along with it as a window group.

If the goal is to produce similarly behaving GUI but only different programming interface (async vs sync), then this will not get the same "sheet" behavior that happens in AsyncFileDialog https://developer.apple.com/design/human-interface-guidelines/macos/windows-and-views/sheets/

[PolyMeilex]

It's a good middle ground, sheet forces us to start an event loop, so I would like to avoid that in sync API if possible.