winrt: Resize window on Windows Phone using EGL

To avoid duplicating code in ANGLE, we can resize the framebuffer in QPA.
This potentially allows us to synchronize rendering to avoid displaying
a frame which is rendered for the new geometry but is displayed with the
old geometry.

Change-Id: I5f3a0634628d9ea4ca73349a02e646eb043bd757
Reviewed-by: Oliver Wolff <oliver.wolff@theqtcompany.com>