Merge fixes from v1.5.3-v1.5.4 into development

[robwalch]

This PR will...

Merge fixes from v1.5.4 into development

• Fix regression in hls.light.js selection (Fix regression in hls.light.js selection #6155) Fixes Video Buffering Issue with Seek Videos using HLS from Cloudflare Stream in plyr.io #6122
• Use average for level sorting and abandon rules check (Use average for level sorting and abandon rules check #6135) Fixes Automatic level selection doesn't work properly when I use hls.light.js #6151
• Use main playlist details to determine start position of audio and subtitle streaming controllers (Align playlists streaming start position with mismatched end-list tags #6189) Fixes HLS.js 1.5.1 doesn't start auto playing some HLS playlists until the user seeks manually #6126
• Fix regression that removed (unofficial) support for startLevel above max level index (Support startLevel above max level index #6190) Fixes Playback doesn't start if startLevel config param value is greater than available number of levels #6172

Why is this Pull Request needed?

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

[robwalch]

going to cherry-pick as #6155 was already picked and is causing a conflict.