videomonitor(win32): bridge ffmpeg/win32api device ids

- Fixes wstring conversion issue when obtaining video capture device
  friendly name, and uses device id when adding/removing devices using
  the usb-pnp monitoring APIs. As the uid suffix reported by the pnp
  api is different from what returns from the device enumerator, we
  strip the uid and make substring searches for device nodes instead
  of exact matches.

Change-Id: Ibe3d79ed0632c663c2b067772ca592d5c5d466e6
Gitlab: #171