[Window] Expose Window.DialogResult as a property

[rabbitism]

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

Both WinForm and WPF expose DialogResult as a public property, user can set it in advance instead of relying on Close(object result) method.
This will allow windows return a proper result even close from CaptionButtons.

Describe the solution you'd like

Expose DialogResult as a public property, if user close it directly with close method or from UI CaptionButtons, it returns this result. If User call Close(result), the result will be automatically assigned to this property and return.

Describe alternatives you've considered

No

Additional context

No response