Support attaching a child to a parent and keep its relative location

[cwensley]

Is your feature request related to a problem? Please describe.
There's no way to "attach" a window to a parent while keeping its location relative to that window, other than on Mac.

Describe the solution you'd like
Some way to attach to a parent, if possible. Other solutions in this case might be to make wrapped Windows of Win32/Mac windows support the LocationChanged/SizeChanged events.

Describe alternatives you've considered
P/invokes for Windows works but is less than ideal. Some solution that is Eto-based would be more cross platform and easier to use.

Additional context
See #2545 for more context