msdk: implement overlay/composite plugin
MediaSDK supports overlay/composite via mfxExtVPPComposite. Develop a msdkoverlay plugin for gst-msdk. The design (i.e. properties and usage) should be similar to vaapioverlay.
MediaSDK supports overlay/composite via mfxExtVPPComposite. Develop a msdkoverlay plugin for gst-msdk. The design (i.e. properties and usage) should be similar to vaapioverlay.