Allow webrtc connection for products

[ERussel]

SUMMARY

Products need WebRTC (RTCPeerConnection) inside the iOS/Android host. The
earlier approach in #379 tried
to gate it behind an app-level permission through the __container__ bridge,
but that gating did not hold up, so it is not the path forward.

Instead, the lockdown container now leaves RTCPeerConnection available to
products rather than deleting it. Access to the camera and microphone stays
protected by the operating system: the user still sees the native permission
prompts before any media is captured.

SOLUTION

• js/container — the TrUAPI-mode lockdown no longer removes
  window.RTCPeerConnection. Products can construct peer connections directly;
  camera and microphone capture (getUserMedia) continues to trigger the
  native OS permission request. The vendored
  ios/truapi-host/.../Resources/truapi-container.js bundle is regenerated to
  match.
• Playground — the WebRTC method requests camera and microphone (device
  permissions) through TrUAPI, then runs getUserMedia +
  RTCPeerConnection.createOffer. It appears in the method browser and the
  diagnosis so the flow can be exercised end to end. It no longer requests a
  separate WebRTC remote permission.

CONTEXT

• WebRTC gating attempt and its conclusion:
  WebRTC gating #379
• companion integration into iOS https://github.com/paritytech/polkadot-app-ios-v2/pull/1351