Modernize WebRTC with promises compatibly with hybrid.

Let me know if I missed anything. Leaving polish of legacy note to others.
This exact wording is one of the key parts of JSEP that took many months to get agrement on. I am strongly apposed to changing this and do not believe there is consens to make this change.  Let me be very lcear this is a huge deal if people wnat to try and open this can of works.