mediafoundation: Add support video capture on UWP app

Merged Seungha Yang requested to merge seungha.yang/gst-plugins-bad:winrt-capture into master
New video capture implementation using WinRT Media APIs for UWP app.
Due to the strict permission policy of UWP, device enumeration and
open should be done via new WinRT APIs and to get permission from users,
it will invoke permission dialog on UI.
Strictly saying, this implementation is not a part of MediaFoundation
but structurally it's very similar to MediaFoundation API.
So we can avoid some code duplication by adding this implementation
into MediaFoundation plugin.

This implementation requires UniversalApiContract version >= 6.0
which is part of Windows 10 version 1803 (Redstone 4)
Edited by Seungha Yang

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