This PR will...

Fixes handling of media element transfer between primary and asset HLS.js instances when abutting interstitials have different strategies for appending media (resetting the media source vs using the primary media source in place) and when the underlying primary content spans multiple discontinuities.

Why is this Pull Request needed?

• Avoids loading and queueing primary init segments for discontinuities obscured by interstitials which could lead improper appends and handling of mixed codecs between primary and interstitial.
• Maintains asset player currentTime after media is detached
• Prevent playback from restarting on schedule change after primary media has ended

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