Date/TimePicker popup gets truncated on small screens with overlay popups

[grokys]

Describe the bug

When running with OverlayPopups = true on a small screen (such as a small embedded device) the DatePicker/TimePicker popup gets truncated:

To Reproduce

Steps to reproduce the behavior:

1. In ControlCatalog.NetCore, Program.cs, enable OverlayPopups = true in the Win32PlatformOptions
2. Run the program and resize the window to its minimum size
3. Open a DatePicker

Expected behavior

The date/time picker popup should be truncated to the available size.

Screenshots

Desktop (please complete the following information):

• OS: All
• Version: master

[grokys]

The problem appears to be that OverlayLayer inherits the measure behavior from Canvas, which measures all children with infinity size. We should probably measure its children using the passed availableSize instead.