Make Named Pipe Server Stream name fit into allowed length on Android

src/libraries/System.IO.FileSystem/tests/FileSystemTest.cs

@@ -61,7 +61,23 @@ public static string GetNamedPipeServerStreamName()
             {
                 return @"LOCAL\" + Guid.NewGuid().ToString("N");
             }
-            return Guid.NewGuid().ToString("N");
+
+            if (PlatformDetection.IsWindows)
+            {
+                return Guid.NewGuid().ToString("N");
+            }
+
+            const int MinUdsPathLength = 104; // required min is 92, but every platform we currently target is at least 104
+            const int MinAvailableForSufficientRandomness = 5; // we want enough randomness in the name to avoid conflicts between concurrent tests
+            string prefix = Path.Combine(Path.GetTempPath(), "CoreFxPipe_");
+            int availableLength = MinUdsPathLength - prefix.Length - 1; // 1 - for possible null terminator
+            Assert.True(availableLength >= MinAvailableForSufficientRandomness, $"UDS prefix {prefix} length {prefix.Length} is too long");
+
+            return string.Create(availableLength, 0, (span, _) =>
+            {
+                for (int i = 0; i < span.Length; i++)
+                    span[i] = (char)('a' + Random.Shared.Next(0, 26));
+            });
         }
 
         /// <summary>