PR #4548 inadvertantly broke mouse button input in the WPF control. This happened due to the extra layer of HWND indirection. The fix is to move the mouse button handling down into the native control where the window messages are now being sent.
This PR hooks up the existing UIA implementation to the WPF control. Some existing code that was specific to the UWP terminal control could be shared so that has been refactored to a common location as well.
## Validation Steps Performed
WPF control was brought up in UISpy and the UIA tree was verified. NVDA was then used to check that screen readers were operating properly.
This adds the WPF control to our project, courtesy of the Visual Studio team.
It re-hosts the Terminal Control components inside a reusable WPF adapter so it can be composed onto C# type surfaces like Visual Studio requires.
