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
Summary
----------
When the same script file gets executed in multiple Runspaces, the RuntimeType generated from the powershell class defined in the file will be shared among those Runspaces. For different Runspaces, different SessionState should be used to run the static methods.
Fix
---
We use the `SessionStateKeeper` to query for the correct `SessionState` to use for a static method call.
We already use `SessionStateKeeper` to track the `Runspace/SessionState` where a PowerShell class is defined, and thus we can leverage this for the static method invocation.
