Fix missing offer in syncState (#1028)

It appears that the server is not using this field anyway, but this
aligns with the other SDKs.

Author: hiroshihorie

.changes/fix-syncstate-offer

@@ -0,0 +1 @@
+patch type="fixed" "Include last server offer in SyncState during reconnection"

lib/src/core/engine.dart

@@ -1231,6 +1231,7 @@ class Engine extends Disposable with EventsEmittable<EngineEvent> {
     required List<String> trackSidsDisabled,
   }) async {
     final previousAnswer = (await subscriber?.pc.getLocalDescription())?.toPBType();
+    final previousOffer = (await subscriber?.pc.getRemoteDescription())?.toPBType();
 
     // Build data channel receive states for reliability
     final dataChannelReceiveStates = <lk_rtc.DataChannelReceiveState>[];
@@ -1245,6 +1246,7 @@ class Engine extends Disposable with EventsEmittable<EngineEvent> {
     }
     signalClient.sendSyncState(
       answer: previousAnswer,
+      offer: previousOffer,
       subscription: subscription,
       publishTracks: publishTracks,
       dataChannelInfo: dataChannelInfo(),

lib/src/core/signal_client.dart

@@ -485,6 +485,7 @@ extension SignalClientRequests on SignalClient {
   @internal
   void sendSyncState({
     required lk_rtc.SessionDescription? answer,
+    required lk_rtc.SessionDescription? offer,
     required lk_rtc.UpdateSubscription subscription,
     required Iterable<lk_rtc.TrackPublishedResponse>? publishTracks,
     required Iterable<lk_rtc.DataChannelInfo>? dataChannelInfo,
@@ -494,6 +495,7 @@ extension SignalClientRequests on SignalClient {
       _sendRequest(lk_rtc.SignalRequest(
         syncState: lk_rtc.SyncState(
           answer: answer,
+          offer: offer,
           subscription: subscription,
           publishTracks: publishTracks,
           dataChannels: dataChannelInfo,