Remove DOM TypeScript type

[ibc]

In tsconfig.json we rely on "dom" TS library. We do it because we need definition of RTCPeerConnection, MediaStream and tons of things only available in browser.

However we also want that mediasoup-client runs in Node (by using mediasoup-client-aiortc for example). And it's a bad idea to use DOM TS types in a lib intended (also) for Node. So:

• We should remove "dom" library from tsconfig.json.
• Define our own types.
• No need to define things like RTCStatsReport. We can make getStats() methods return ReturnType<xxx>. Well, not sure if this is doable. ReturnType of what?

[ibc]

Actually I'm gonna close this task. Despite mediasoup-client can work in Node it heavily rely on WebRTC API. For example, Producer.ts depends on many "dom" types such as MediaStreamTrack, RTCRtpSender, etc:

/**
 * Associated RTCRtpSender.
 */
get rtpSender(): RTCRtpSender | undefined {
    return this._rtpSender;
}

/**
 * The associated track.
 */
get track(): MediaStreamTrack | null {
    return this._track;
}

We cannot replace them with "abstract" types because they are what they are.

The thing is that, when running in Node, the mediasoup-client handler (such as mediasoup-client-aiortc) must be ready to handle and produce objects with those types.