WinRT: Trim() on suspend is missing, without it the app cannot pass store certification

Windows Store certification requires that the application trim its graphics resources on suspend. There are at least two ways to do this:

1. Add an extension to ANGLE to return the DXGIDevice from eglQuerySurfacePointerANGLE. Then get the device pointer and call Trim() inside the winrt QPA plugin.
2. Add a suspending callback inside ANGLE, and call Trim() there.

The downsides of the approach #1 are that it requires more than one patch, and that it requires the platform plugin to link to DXGI. The downsides of approach #2 are that it is introduces another fairly invasive patch to ANGLE, and that the developer has no control over Trim() being called (or not called).