Normalize copyright and license header

[dev-experience]

Changes:

• Remove "All rights reserved."
• Normalize copyright/license header in all files

Following the PR 12190 "Update copyright notice to latest guidance" from PowerShell/PowerShell repo: https://github.com/PowerShell/PowerShell/pull/12190

Latest guidance is to not have the "All rights reserved." sentence. Changes are based on the Contributing guidelines of PowerShell/PowerShell: https://github.com/PowerShell/PowerShell/blob/master/.github/CONTRIBUTING.md#pull-request---submission The reason is to avoid ambiguity of the combination of MIT license and "All rights reserved"

Useful links:

• https://github.com/PowerShell/PowerShell/issues/2129
• https://opensource.stackexchange.com/questions/2121/mit-license-and-all-rights-reserved