[Proposal] Enhancements to WindowStartupLocation

[ngarside]

Looking for feedback if this would be wanted in Avalonia.

Is your feature request related to a problem? Please describe.

I need a way to open windows in the corner of the screen, with a margin separating them from the screen edge and taskbar.

Describe the solution you'd like

Extend WindowStartupLocation

public enum WindowStartupLocation
{
	// Existing
	Manual,
	CenterScreen,
	CenterOwner,

	// New
	TopLeft,
	TopRight,
	BottomRight,
	BottomLeft,
}

For the screen edge margin, I'd piggyback off of Layoutable.Margin (which as far as I can tell isn't used by Window currently).

I'm not sure if/how it would work with owned windows, or if it even should work with them.

Describe alternatives you've considered

I was planning to create a Window subclass for my own project, so if this is outside the scope of Avalonia itself then I'll just continue with that.

Additional context

This would likely have issues on wayland, although I haven't checked how CenterScreen works on wayland, so maybe it's no different.

[kekekeks]

For Wayland that feature won't work at all, so don't worry much about that.