Implement MediaDevices.GetSupportedConstraints with real capability flags

[General-Fault]

Summary

MediaDevices.GetSupportedConstraints() currently returns a default MediaTrackSupportedConstraints instance and does not map actual supported constrainable properties from runtime/platform capabilities.

Why

Callers need accurate feature flags to know which constraints can be relied on before constructing advanced constraints.

Scope

• Implement real supported-constraint reporting for media capture.
• Wire interop/managed mapping so returned flags reflect actual supported behavior.

Related files

• WebRtcInterop\Media\MediaDevices.cpp
• WebRtcNet.Api\Media\MediaDevices.cs
• WebRtcNet.Api\Media\MediaTrackSupportedConstraints.cs