Restore content key session support in Core Business

[defagos]

As an app developer I want to be able to offer offline playback for DRM-protected content to users of my product. This requires the use of AVContentKeySession.

Acceptance criteria

• AVContentKeySession is always used for playing SRG SSR DRM-protected content.

Tasks

• Revert changes from Impossible to recover from DRM error #1232.
• Update known issues (problem affects iOS 18 and early versions of 26).