Feature: Unregister Stretchy block variations

[colinswinney]

Description of the Change

This PR removes the Stretchy block variations added to WP 6.9 on the Heading and Paragraph blocks. Because the accessibility of such a feature can be easily mismanaged, this creates an "opt-in" scenario to ensure its desirability.

10up-block-theme before

10up-block-theme after

10up-theme before

10up-theme after

Closes N/A

How to test the Change

1. Pull the branch and run npm run build
2. Open the block editor
3. View the inserter - you should no longer see the Stretchy Heading or Paragraph variations in either theme

Changelog Entry

Removed - Stretchy block variations for Heading and Paragraph blocks due to accessibility concerns

Credits

Props @colinswinney

Checklist:

• I agree to follow this project's Code of Conduct.
• I have updated the documentation accordingly.
• I have added Critical Flows, Test Cases, and/or End-to-End Tests to cover my change.
• All new and existing tests pass.