Match LiveKit participants against all backend identities

A member authenticated through the legacy JWT endpoint publishes under a
`user:device` identity, while one authenticated through the default
endpoint publishes under a hashed identity. Both are listed in the
membership's backend identities, so match against the whole list rather
than only the primary one.

Element Call's test membership mock, matching the SDK's RTCMember.

src/utils/test.ts

@@ -224,7 +224,7 @@ export function mockRtcMembership(
   deviceId: string,
   customOverwrites?: {
     rtcBackendIdentity?: string;
-    /** Every identity the member may have in LiveKit, when more than one. */
+    /** Every identity the member may have on its transport, where more than one. */
     backendIdentities?: string[];
     callId?: string;
     fociPreferred?: Transport[];
@@ -471,6 +471,7 @@ export function mockRTCMember(
         };
   const base = {
     rtcBackendIdentity: membership.rtcBackendIdentity,
+    backendIdentities: membership.backendIdentities,
     userId: membership.userId,
     deviceId: membership.deviceId,
     memberId: membership.memberId,