Multi-key handling

[robwalch]

This PR will...

• Group media key sessions by key tag (EXT-X-KEY) URI, and group all parsed key tags (LevelKey instances) and their key-ids in eme-controller session-context objects.
• Fix key-status errors being ignored after key is usable.
• Warn when "output-restricted" key status is received on level with HDCP-LEVEL=NONE
• Fix error handling after after encountering same key URI that errored previously
• Fix escalation of unresolved level removal to fatal

Why is this Pull Request needed?

• Reduces license requests / sessions when multiple-keys are delivered in a single PSSH/URI
• Fixes edge cases where key status updates were not handled

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

If you've recently reported issues related to EME playback, please review and leave feedback if you are able to test. Thanks!

• @hongfeih-es
  • The playback ends when the "keySystemStatusInternalError" occurs #7413
  • extract key id incorrectly from key statuses when using PlayReady #7508
• @ShubhamSharma2311
  • Fix PlayReady key endianness #7510
• @mudit2108
  • HDCP error when playing manifests with both HD and SD levels #7469
• @grabofus
  • Fix requireKeySystemAccessOnStart with live #7383

Resolves issues:

• Resolves Multi-key handling #7474
• Includes enhancements for HDCP error when playing manifests with both HD and SD levels #7469

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]

• Rebase over Error handling for PlayReady key with no status change #7527

[robwalch]

• Follow up regarding Fix issue where some devices not works with playready #7631

TODO:

Address the change made in #7631 which handles the case where keyId in keyStatuses does not require endianness to be changed.

Rather than cherry-pick #7631, consider looking for a match in mediaKeySessionContext (this might require iterating through all keyStatuses keys) and if a match is found, do not change endianness on all key status keys (ever).

An optional configuration setting that is undefined by default and only set if unset could be added to specify here whether or not to change endianness. The lookup for a match described above would only be run if this option is unset.