Update copyright and license headers (#6134)

Based on standard practices, we need to have a copyright and license notice at the top of each source file. Removed existing copyrights and updated/added copyright notices for .h, .cpp, .cs, .ps1, and .psm1 files.

Updated module manifests for consistency to have Author = "PowerShell" and Company = "Microsoft Corporation". Removed multiple line breaks.

Separate PR coming to update contribution document for new source files: #6140

Manually reviewed each change.

Fix #6073

src/System.Management.Automation/namespaces/FileSystemSecurity.cs

@@ -1,6 +1,5 @@
-/********************************************************************++
-Copyright (c) Microsoft Corporation. All rights reserved.
---********************************************************************/
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
 
 using System;
 using System.IO;