Enable SpriteVisuals to work along side HWNDs so that Angle rendered content can be
hosted with Windows::UI::Composition APIs or XamlIslands in desktop Win32 applications.

Includes a whitebox test, verified Win7 compatibility

For more info see:
https://docs.google.com/document/d/1ggv6H-aK1a3pXNMTtMF6h0Bv0rulIeBpBxBBCJYR6Zs/edit?usp=sharing

Bug: angleproject:2947
Change-Id: Id005739553be2a6268cd4543f1b07aaf89760422
Reviewed-on: https://chromium-review.googlesource.com/c/1236844
Commit-Queue: James Clarke <james.clarke@microsoft.com>
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>