Replace mux.js for CEA parsing

[joeyparrish]

Have you read the FAQ and checked for duplicate open issues?
Yes

Is your feature request related to a problem? Please describe.
Using mux.js for transmuxing makes sense, as we do not want to support TS streams long-term. Using mux.js for CEA captions is different, since broadcast TV caption standards are not going away any time soon.

Describe the solution you'd like
We should own our own CEA parser so that apps do not need an additional dependency for caption parsing. We can keep mux.js as an optional dependency for transmuxing TS content.

Describe alternatives you've considered

1. Continue using mux.js for captions (no change from today)
2. Use another existing parser (still a third-party dep, but now multiple)