Proposal: Add FrameworkElement.LayoutTransform

[michael-hawker]

Proposal: Add FrameworkElement.LayoutTransform

Summary

LayoutTransform is missing from FrameworkElement. This makes it harder to port WPF code and perform some advanced transforms which need to impact layout to work. This is also needed for future Expander (#3492) improvements.

Rationale

LayoutTransform was available in WPF and provided a useful way for transforming elements in ways that effect layout. This is useful for certain controls like Expanders or if rotating rectangular elements.

While there is a stop-gap in the WCT it is a wrapper and not part of the element like the original in WPF. It also isn't a perfect re-implementation because of this inversion. It'd be better if it was built-in to part of the framework like RenderTransform.

Functional Requirements

• Forwards compatible with WPF
• Supports Expander scenarios

[michael-hawker]

@predavid this needs the wpf tracking label too.

FYI @ejserna @chrisglein