Fix multiple instances of a game being allowed to start concurrently

Regressed with ppy#6442.

Was not visible in test coverage because as per the inline comment, this
is an exceptional case where two different processes bind.

I'm not sure how to add test coverage for this, but I have tested
manually on both windows and macOS.

osu.Framework/Platform/NamedPipeIpcProvider.cs

@@ -34,6 +34,8 @@ public class NamedPipeIpcProvider : IDisposable
 
         private NamedPipeServerStream? pipe;
 
+        private Mutex? mutex;
+
         /// <summary>
         /// Create a new provider.
         /// </summary>
@@ -57,7 +59,17 @@ public bool Bind()
 
             try
             {
-                pipe = new NamedPipeServerStream($"osu-framework-{pipeName}", PipeDirection.InOut);
+                string name = $"osu-framework-{pipeName}";
+
+                // Named pipes from different processes are allowed to coexist, but we don't want this for our purposes.
+                // Using a system global mutex allows ensuring that only one osu!framework project using the same pipe name
+                // will be able to bind.
+                mutex = new Mutex(false, $"Global\\{name}", out bool createdNew);
+
+                if (!createdNew)
+                    return false;
+
+                pipe = new NamedPipeServerStream(name, PipeDirection.InOut, 1);
 
                 listenTask = listen(pipe);
 
@@ -202,6 +214,8 @@ public void Dispose()
 
             cancellationSource.Cancel();
 
+            mutex?.Dispose();
+
             if (listenTask != null)
             {
                 try