Use non-deprecated method of re-processing MatrixRTCSession keys (#2646)

* Handle case of encryption key for an index to be undefined

As per https://github.com/matrix-org/matrix-js-sdk/pull/4423 the key can be undefined and so we should handle this rather than waiting for SubtleCrypto.importKey() to fail.

* Use release version of matrix-js-sdk

Diff is https://github.com/matrix-org/matrix-js-sdk/compare/baa6d135065637c9769c61325c69709d3618f5f1...v34.7.0

* Use RTCSession. reemitEncryptionKeys()

* Add some test coverage whilst we are here

* Add some test coverage whilst we are here

* Lint

package.json

@@ -84,7 +84,7 @@
     "livekit-client": "^2.5.7",
     "lodash": "^4.17.21",
     "loglevel": "^1.9.1",
-    "matrix-js-sdk": "matrix-org/matrix-js-sdk#baa6d135065637c9769c61325c69709d3618f5f1",
+    "matrix-js-sdk": "^34.7.0",
     "matrix-widget-api": "^1.8.2",
     "normalize.css": "^8.0.1",
     "observable-hooks": "^4.2.3",