Follow up with Microsoft: UWP Window Capture may fail to capture new windows

Due to a weakness in winrt window capturing, window capture may fail on newly created windows. This is particularly visible in unit tests. 

For reproducer, see jogerh/WindowCaptureBug (github.com). Bug is reported to Microsoft: winrt::Windows::Graphics::Capture::IGraphicsCaptureItemInterop::CreateForWindow often fails on new windows. - Developer Community (visualstudio.com)

See also https://aka.ms/AAm41lt

In QtMultimedia, we remediate this issue by retrying the problematic function call until it succeeds. Still, the likelihood of this retry being necessary is low, because window capturing will likely not start immediately after window creation in normal use cases.