Support binary payload in RTCDataChannel

[js-seo]

• Fix sending binary data a6eb5e3
  • data.buffer which was at 157 line in RTCDataChannel.js before this change was becoming {} when it gets to the WKWebViewRTC.swift through the bridge. So data was not being sent as expected.
  • I encoded it to string before passing, and then decoded afterwards.
• Fix receiving binary data 5afeb61
  • Encode and decode received data just like the sent data.
  • data field of the first argument(event) of RTCDataChannel.prototype.onmessage is now ArrayBuffer following the native browser API, other than { Type: 'ArrayBuffer', Data: string }

[hthetiot]

Interesting PR, I may back port this feature on https://github.com/cordova-rtc/cordova-plugin-iosrtc

[noahmehl]

@js-seo WOW! Thanks so much for contributing this! We will review asap!