Make IPC port configurable via HostOptions

osu.Framework/HostOptions.cs

@@ -15,6 +15,11 @@ public class HostOptions
         /// </summary>
         public bool BindIPC { get; set; }
 
+        /// <summary>
+        /// The IPC port to bind. See <see cref="IIpcHost"/> for more details on usage.
+        /// </summary>
+        public int IPCPort { get; set; } = 45356;
+
         /// <summary>
         /// Whether this is a portable installation. Will cause all game files to be placed alongside the executable, rather than in the standard data directory.
         /// </summary>

osu.Framework/Platform/DesktopGameHost.cs

@@ -15,15 +15,15 @@ namespace osu.Framework.Platform
 {
     public abstract class DesktopGameHost : SDL2GameHost
     {
-        public const int IPC_PORT = 45356;
-
         private TcpIpcProvider ipcProvider;
         private readonly bool bindIPCPort;
+        private readonly int ipcPort;
 
         protected DesktopGameHost(string gameName, HostOptions options = null)
             : base(gameName, options)
         {
             bindIPCPort = Options.BindIPC;
+            ipcPort = Options.IPCPort;
             IsPortableInstallation = Options.PortableInstallation;
         }
 
@@ -63,7 +63,7 @@ private void ensureIPCReady()
             if (ipcProvider != null)
                 return;
 
-            ipcProvider = new TcpIpcProvider(IPC_PORT);
+            ipcProvider = new TcpIpcProvider(ipcPort);
             ipcProvider.MessageReceived += OnMessageReceived;
 
             IsPrimaryInstance = ipcProvider.Bind();