Fix button block contrast checker

[talldan]

Proposed changes:

Fixes an issue with the Jetpack Button block's contrast checking. Currently the contrast checker only works when the user has set both the background and text color.

If the user changes only one of the text or background color in a way that causes a contrast issue, the checker doesn't display a warning.

Some history - this functionality was previously handled by a higher order component - applyFallbackStyles / withFallbackStyles. #41139 removed the HOC because it had a few issues:

• It added a wrapping <div> around the block which breaks a range of styles
• It didn't check the correct element for background colors
• It didn't update when the block's css changes (e.g if inline styles or a class are added).

This PR introduces a small hook to replace the applyFallbackStyles / withFallbackStyles to keep the contrast checker working.

Other information:

• Have you written new tests for your changes, if applicable?
• Have you checked the E2E test CI results, and verified that your changes do not break them?
• Have you tested your changes on WordPress.com, if applicable (if so, you'll see a generated comment below with a script to run)?

Does this pull request change what data or activity we track or use?

No

Testing instructions:

1. Add a contact form block
2. Select the button in the form
3. Change only the text color to something that conflicts with the button background (e.g. if there's a black background, set the text to black). Or the opposite, change only the background color.
4. Observe the contrast checker should be displayed. (in trunk it doesn't show).

[github-actions]

Are you an Automattician? Please test your changes on all WordPress.com environments to help mitigate accidental explosions.

• To test on WoA, go to the Plugins menu on a WordPress.com Simple site. Click on the "Upload" button and follow the upgrade flow to be able to upload, install, and activate the Jetpack Beta plugin. Once the plugin is active, go to Jetpack > Jetpack Beta, select your plugin, and enable the fix/button-fallback-contrast-checking branch.

• To test on Simple, run the following command on your sandbox:

  bin/jetpack-downloader test jetpack fix/button-fallback-contrast-checking
  

Interested in more tips and information?

• In your local development environment, use the jetpack rsync command to sync your changes to a WoA dev blog.
• Read more about our development workflow here: PCYsg-eg0-p2
• Figure out when your changes will be shipped to customers here: PCYsg-eg5-p2

[github-actions]

Thank you for your PR!

When contributing to Jetpack, we have a few suggestions that can help us test and review your patch:

• ✅ Include a description of your PR changes.
  
• ✅ Add a "[Status]" label (In Progress, Needs Team Review, ...).
  
• ✅ Add a "[Type]" label (Bug, Enhancement, Janitorial, Task).
  
• ✅ Add testing instructions.
  
• ✅ Specify whether this PR includes any changes to data or privacy.
  
• ✅ Add changelog entries to affected projects
  

This comment will be updated as you work on your PR and make changes. If you think that some of those checks are not needed for your PR, please explain why you think so. Thanks for cooperation 🤖

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The e2e test report can be found here. Please note that it can take a few minutes after the e2e tests checks are complete for the report to be available.

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Follow this PR Review Process:

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Jetpack plugin:

The Jetpack plugin has different release cadences depending on the platform:

• WordPress.com Simple releases happen semi-continuously (PCYsg-Jjm-p2).
• WoA releases happen weekly.
• Releases to self-hosted sites happen monthly. The next release is scheduled for none scheduled (scheduled code freeze on undefined).

If you have any questions about the release process, please ask in the #jetpack-releases channel on Slack.

[github-actions]

Code Coverage Summary

Coverage changed in 1 file.

File	Coverage	Δ%	Δ Uncovered
projects/plugins/jetpack/extensions/blocks/button/edit.js	9/10 (90.00%)	1.11%	0 💚

1 file is newly checked for coverage.

File	Coverage
projects/plugins/jetpack/extensions/blocks/button/use-fallback-colors.js	7/12 (58.33%) 💚

Full summary · PHP report · JS report