Add networkInformation object to DLASE

[compulim]

Changelog

Added

• Direct Line Streaming: Added networkInformation option to assist detection of connection issues, by @compulim, in PR #412

Designs

On iOS/iPadOS Safari, when connection change from Wi-Fi to cellular (say, walking away from coffee shop), the WebSocket object did not emit error event. It simply stalled. This only repros on iOS/iPadOS. It did not repro on Android Chrome.

To detect network type change, we could use networkInformation.type. However, Network Information API is not implemented in Safari.

We are adding a new option to allow web developers to provide a polyfill of W3C Network Information API. They could implement the polyfill using Server-Sent Events or native calls to NWPathMonitor.

When the NetworkInformation instance detected network change, it should:

1. Change type to current network type, such as "cellular", "wifi", "unknown", or "none" (offline)
2. Emit change event

Upon receiving the change event with type property changed, the chat adapter would terminate the current Web Socket connection and retries.

Currently, despite Network Information API is implemented in modern browsers, the type property may not be implemented. A simple polyfill for the type property:

Object.defineProperty(navigator.connection, 'type', {
  get() {
    return this.downlink ? 'unknown' : 'none';
  }
});

Specific changes

• Added networkInformation to DirectLineStreaming options