feature: Add GetStreams to AudioClient (#1588)

* Added GetStreams

* Change return type

* Change return type on the interface

Co-authored-by: Paulo <pnmanjos@hotmail.com>

src/Discord.Net.Core/Audio/IAudioClient.cs

@@ -1,4 +1,5 @@
-using System;
+using System;
+using System.Collections.Generic;
 using System.Threading.Tasks;
 
 namespace Discord.Audio
@@ -20,6 +21,9 @@ namespace Discord.Audio
         /// <summary> Gets the estimated round-trip latency, in milliseconds, to the voice UDP server. </summary>
         int UdpLatency { get; }
 
+        /// <summary>Gets the current audio streams.</summary>
+        IReadOnlyDictionary<ulong, AudioInStream> GetStreams();
+
         Task StopAsync();
         Task SetSpeakingAsync(bool value);