RTCSession cleanup: deprecate getKeysForParticipant() and getEncryption(); add emitEncryptionKeys() (#4427)
* RTCSession cleanup: deprecate getKeysForParticipant() and getEncryption(); add emitEncryptionKeys()
* Clarify comment
* Feedback from code review
* Update src/matrixrtc/MatrixRTCSession.ts
Co-authored-by: Andrew Ferrazzutti <andrewf@element.io>
* Fix test
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Co-authored-by: Andrew Ferrazzutti <andrewf@element.io>