It's only used for the UMD bundle.

* feat(multi-stream-support) Handle SDP munging for multiple local/remote streams/ep.
A new SDPSimulcast class is added for handling SDP munging for local and remote descriptions to handle multiple streams for both local and remote endpoints. This new class will be used only for unified plan implentation. The sdp-simucast npm package will be used for plan-b and deprecated later when all the clients switch to unified plan.

* fix(build) fix building with TS code

Use the Babel preset for the webpack bundle since Babel 7 already
understands TS and ts-loader uses tsc instead, which we configure
differently.

* squash: Add unit test and address review comments.

Co-authored-by: Saúl Ibarra Corretgé <saghul@jitsi.org>

This should allow us to monitor the progress when comparing them to hand-crafted
ones.

This is just the stepping stone towards the goal of eventually having
lib-jitsi-meet fully written in JS.

- introduce ts-loader for webpack
- webpack will continue generating the UMD bundle
- tsc will generate an ES6 module
- output all bundles to dist/