UE-14641 - Fix PushMenu() to use QueryPopupMethod()
Pretty big refactor
Adds IMenu as way to identify menus. Replaces referring to menus as SWindows.
Lots of uses of PushMenu() fixed up to match new API
#codereview Nick.Atamas
[CL 2579277 by Chris Wood in Main branch]
Slate TPanelChildren, TSlotlessChildren are no longer full-fledged arrays; removed any unused Array API.
Fixed up a lot of improper use cases.
This better encapsulates the action of adding/removing Slate Widgets from the runtime tree as a Slate Core concern.
Alows us to add parent pointers in the future with significantly less effort.
#codereview Wes.Hunt
#codereview Nick.Darnell
#codereview Matt.Kuhlendschmidt
#codereview Justin.Sargent
[CL 2234301 by Nick Atamas in Main branch]
* Paint is now the non-virtual entry point to OnPaint to support required pre/post functionality. Widgets override OnPaint as usual, but calls to tell a widget to paint should be "Paint" not "OnPaint".
* ArrangeChildren -> OnArrangeChildren. ArrangeChildren is now the non-virtual entry point for the same reason as Paint/OnPain.
* OnPaint and OnArrageChildren are now private so they are not accidentally called.
* Added Stats for Paint time and ArrangeChildren time.
#BUN
#codereview:nick.atamas,max.preussner
[CL 2086158 by Wes Hunt in Main branch]
#summary Replaced instances of DragDrop::IsTypeMatch with FDragDropEvent::GetOperationAs()
#note Please change any instances of DragDrop::IsTypeMatch for the templated FDragDropEvent::GetOperationAs<>() or FDragDropOperation::IsOfType<>() where necessary
#proj Editor
#branch UE4
#reviewedby Nick.Atamas
[CL 2042222 by Andrew Rodham in Main branch]
