fix(controls): Support ExpandDirection and clicking anywhere on header to expand (Expander.xaml)

[Alex4SSB]

WPF expander has a built-in property for ExpandDirection, which sometimes can be useful. Also, clicking in the bottom/top 1/4 of the expander header's height doesn't expand it.
Also, there was a TODO in the gallery Expander page - that's dealt with now, at least for the regular Expander, not for the CardExpander.

Pull request type

Please check the type of change your PR introduces:

• Update
• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes

What is the current behavior?

1. There is no support for the built-in Expander property ExpandDirection.
2. Only the actual height occupied by the header ToggleButton content (ex.: text) is clickable to affect IsExpanded state.
   Issue Number: N/A

What is the new behavior?

The Expander now fully supports ExpandDirection:

• ToggleButton and ContentPresenter are docked accordingly
• BorderThickness and CornerRadius are adjusted accordingly
• RenderTransform direction is adjusted accordingly
• Clicking anywhere on the header will now affect IsExpanded state

Notes

Currently in the gallery app, Down (default), Left and Right directions work correctly, but Up lacks correct animation, until cycled through Left / Right first. Shouldn't a problem for most library users though, as an Expander rarely has its direction changed at run-time like in the gallery.