This PR will...

Fix Widevine key management

• Use the Key ID in EXT-X-KEY KEYID when available for Widevine
• Deduplicate key data with the same attributes when parsing media playlists
• Ignore data in "encrypted" event (hls.js can't reliably parse the key id from PSSH without a Widevine protobuf parser)

Why is this Pull Request needed?

The Widevine PSSH key id parsing in hls.js (read the 16 bytes 6 bytes back from the end) assumes no optional fields and can't always extract the key id that vendors are including in the playlist (the key id matching tenc box bytes and KEYID attribute value). Since it is difficult to match the "encrypted" event initdata to key tags in the playlist without being able to extract a matching key id, it is better to ignore the event and rely only on key data which is required to be included in HLS media playlists.

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

Resolves issues:

Fixes #7369

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