Add videoCodec field to videoPreference options

[robwalch]

This PR will...

• Add videoCodec field to config.videoPreference
• Improve SDR/HDR initial selection results
  • Don't narrow allowed video-ranges to one that is not available
  • Pick lowest in start tier regardless of "skip candidate" rules as long as "can switch within tolerance" check passes
• Fix return value for setSubtitleOption and undefined->null type for setAudioOption

Why is this Pull Request needed?

• HLS Interstitials Support #5730 with child player instances that match primary player SourceBuffer configuration

Are there any points in the code the reviewer needs to double check?

Resolves issues:

Checklist

• changes have been done against master branch, and PR does not conflict
• new unit / functional tests have been added (whenever applicable)
• API or design changes are documented in API.md