Add license headers. (#26009)

Any *.cs file found without the usual license header has it added except:

1. Files that note they are auto-generated.
2. Files with a different header (unless it is very close to the usual,
in which case adjust for typos and old versions).
3. FxCopBaseline.cs files.

Author: JonHanna

src/Common/perf/PerfRunner/PerfRunner.cs

@@ -1,3 +1,7 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
 using System.IO;
 using System.Reflection;
 using System.Collections.Generic;
@@ -27,4 +31,4 @@ private static IEnumerable<string> GetTestAssemblies()
     {
         return Directory.EnumerateFiles(".", "*.Performance.Tests.dll");
     }
-}
+}

src/Common/src/System/Data/Common/DbConnectionOptions.Common.cs

@@ -1,3 +1,7 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Globalization;
@@ -645,4 +649,4 @@ internal NameValuePair ReplacePasswordPwd(out string constr, bool fakePassword)
             return head;
         }
     }
-}
+}

src/Common/tests/System/Xml/ModuleCore/XunitTestCase.cs

@@ -1,4 +1,8 @@
-using System;
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;

src/Microsoft.CSharp/src/Microsoft/CSharp/RuntimeBinder/ArgumentObject.cs

@@ -1,3 +1,7 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
 using System;
 using System.Diagnostics;
 

src/Microsoft.CSharp/src/Microsoft/CSharp/RuntimeBinder/ICSharpBinder.cs

@@ -1,3 +1,7 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
 using System;
 using Microsoft.CSharp.RuntimeBinder.Semantics;
 
@@ -21,4 +25,4 @@ internal interface ICSharpBinder
         BindingFlag BindingFlags { get; }
         string Name { get; }
     }
-}
+}

src/SharedFrameworkValidation/RestoreSDKProject/Dummy.cs

@@ -1,4 +1,8 @@
-using System;
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
 
 namespace Dummy
 {

src/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableSortedDictionary_2.Node.cs

@@ -1,3 +1,6 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
 
 using System.Collections.Generic;
 using System.Diagnostics;

src/System.Collections.Specialized/tests/StringDictionary/StringDictionary.GetEnumeratorTests.cs

@@ -1,4 +1,4 @@
-// Licensed to the .NET Foundation under one or more agreements.---
+// Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 

src/System.Composition.TypedParts/tests/ReflectionTests.cs

@@ -1,4 +1,8 @@
-using System.Collections.Concurrent;
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Collections.Concurrent;
 using System.Composition.Hosting;
 using System.Threading;
 using Xunit;

src/System.Configuration.ConfigurationManager/src/System/Configuration/SpecialSettingAttribute.cs

@@ -1,8 +1,9 @@
-using System;
-// Licensed to the .NET Foundation under one or more agreements.
+// Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System;
+
 namespace System.Configuration
 {
     /// <summary>