[ImageCapture] Implement platform support for Windows MediaFoundation backend

Image capture functionality is already present on Windows in DirectShow
backend and on Linux and CrOS. This CL adds the platform support also to
the MediaFoundation backend for Windows.

Spec: https://w3c.github.io/mediacapture-image/

Bug: 1049100
Change-Id: I3712ec76efec7fa4ecd40da3661bf0fa40966cdc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2162745
Reviewed-by: Rijubrata Bhaumik <rijubrata.bhaumik@intel.com>
Reviewed-by: Guido Urdaneta <guidou@chromium.org>
Commit-Queue: Eero Häkkinen <eero.hakkinen@intel.com>
Cr-Commit-Position: refs/heads/master@{#765958}