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 baa6d13506...v34.7.0

* Use RTCSession. reemitEncryptionKeys()

* Add some test coverage whilst we are here

* Add some test coverage whilst we are here

* Lint

src/e2ee/matrixKeyProvider.ts

@@ -35,15 +35,8 @@ export class MatrixKeyProvider extends BaseKeyProvider {
     );
 
     // The new session could be aware of keys of which the old session wasn't,
-    // so emit a key changed event.
-    for (const [
-      participant,
-      encryptionKeys,
-    ] of this.rtcSession.getEncryptionKeys()) {
-      for (const [index, encryptionKey] of encryptionKeys.entries()) {
-        this.onEncryptionKeyChanged(encryptionKey, index, participant);
-      }
-    }
+    // so emit key changed events
+    this.rtcSession.reemitEncryptionKeys();
   }
 
   private onEncryptionKeyChanged = (