Support set background color for View

[jctaoo]

view.backgroundColor = xx is not work currently

[compnerd]

Each view has a hWnd associated with it. It should be possible to create a new solid brush and set that via SetWindowLongPtrW. I don't remember if we have a lifetime wrapper for brushes, but that should be pretty easy to create via the generic ManagedHandle type. A patch for this would be a nice addition.