Accept both 'implementation' and 'impl' parameters for GF()

[adnanbhat7]

1.Changed primary parameter from impl to implementation in docstrings
2.Marked impl as deprecated (backwards compatibility)
3.Updated examples to use implementation instead of impl
4.Added examples showing both parameters work
5. clean commit history
@nbruin review this

📝 Checklist

• The title is concise and informative.
• The description explains in detail what this PR is about.
• I have linked a relevant issue or discussion.
• I have created tests covering the changes.
• I have updated the documentation and checked the documentation preview.

⌛ Dependencies

related to #41123