Align Host API access with interop MediaDevices/PeerConnection shims

[General-Fault]

Summary

• add WebRtcNet.Host as a non-browser API root for MediaDevices and peer connection creation
• convert API MediaDevices contract to abstract class and route BasicVideoChat usage through Host
• split interop MediaDevices implementation/factory into dedicated files and include them in shared vcxitems
• keep peer-connection interop in compile-first shim mode while wiring factory creation through RtcPeerConnectionFactory
• merge origin/main project-structure cleanup from Normalize project configuration and platform mappings #42 and reconcile touched project/shared item files

Validation

• BasicVideoChat builds with VS MSBuild for both target frameworks:

et48

et10.0-windows

BugzId:43