chore: expose websockets (#2201)

* chore: websockets. Minimalist UI to use WebSockets

* fix: adjusting #ifdef on transport version to allow building non-webgl platforms with UTP 2.0

* fix: addressing build issue where WebGL platform requires different name for UTP symbols

* fix: emitting a warning and switching to WebSockets if uers don't, on WebGL platform

* Addressing PR review comments

* Addressing PR review comments

* Update com.unity.netcode.gameobjects/CHANGELOG.md

Co-authored-by: Fatih Mar <mfatihmar@gmail.com>

Co-authored-by: Fatih Mar <mfatihmar@gmail.com>

Author: jeffreyrainy

com.unity.netcode.gameobjects/CHANGELOG.md

@@ -9,6 +9,10 @@ Additional documentation and release notes are available at [Multiplayer Documen
 
 ## [Unreleased]
 
+### Added
+
+- Added WebSocket support when using UTP 2.0 with `UseWebSockets` property in the `UnityTransport` component of the `NetworkManager` allowing to pick WebSockets for communication. When building for WebGL, this selection happens automatically. (#2201)
+
 ### Changed
 
 - The debug simulator in `UnityTransport` is now non-deterministic. Its random number generator used to be seeded with a constant value, leading to the same pattern of packet drops, delays, and jitter in every run. (#2196)

com.unity.netcode.gameobjects/Runtime/Transports/UTP/UnityTransport.cs

@@ -150,6 +150,18 @@ private enum State
         [SerializeField]
         private ProtocolType m_ProtocolType;
 
+#if UTP_TRANSPORT_2_0_ABOVE
+        [Tooltip("Whether or not to use WebSockets as Network Interface")]
+        [SerializeField]
+        private bool m_UseWebSockets = false;
+
+        public bool UseWebSockets
+        {
+            set => m_UseWebSockets = value;
+            get => m_UseWebSockets;
+        }
+#endif
+
         [Tooltip("The maximum amount of packets that can be in the internal send/receive queues. Basically this is how many packets can be sent/received in a single update/frame.")]
         [SerializeField]
         private int m_MaxPacketQueueSize = InitialMaxPacketQueueSize;
@@ -1365,7 +1377,23 @@ public void CreateDriver(UnityTransport transport, out NetworkDriver driver,
 #endif
                 heartbeatTimeoutMS: transport.m_HeartbeatTimeoutMS);
 
+#if UTP_TRANSPORT_2_0_ABOVE
+            if (m_UseWebSockets)
+            {
+                driver = NetworkDriver.Create(new WebSocketNetworkInterface(), m_NetworkSettings);
+            }
+            else
+            {
+#if UNITY_WEBGL
+                Debug.LogWarning($"WebSockets were used even though they're not selected in NetworkManager. You should check {nameof(UseWebSockets)}', on the Unity Transport component, to silence this warning.");
+                driver = NetworkDriver.Create(new WebSocketNetworkInterface(), m_NetworkSettings);
+#else
+                driver = NetworkDriver.Create(new UDPNetworkInterface(), m_NetworkSettings);
+#endif
+            }
+#else
             driver = NetworkDriver.Create(m_NetworkSettings);
+#endif
 
 #if MULTIPLAYER_TOOLS_1_0_0_PRE_7
 #if UTP_TRANSPORT_2_0_ABOVE