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

test/powershell/engine/Help/HelpSystem.Tests.ps1

@@ -1,4 +1,6 @@
-#
+# Copyright (c) Microsoft Corporation. All rights reserved.
+# Licensed under the MIT License.
+#
 # Validates Get-Help for cmdlets in Microsoft.PowerShell.Core.
 
 function UpdateHelpFromLocalContentPath
@@ -164,7 +166,6 @@ Describe "Validate that Get-Help returns provider-specific help" -Tags @('CI', '
         $noun = $helptest.noun
         $pending = $helptest.pending
 
-
         It -Pending:$pending "Shows contextual help when Get-Help is invoked for provider-specific path (Get-Help -Name $verb-$noun -Path $path)" {
 
             # Path should exist or else Get-Help will fallback to default help text