feat: Toggle editor theme styles via feature flag

[dcalhoun]

Provide experimental support for the editor WYSIWYG feature.

Fixes https://github.com/Automattic/dotcom-forge/issues/9450.

Testing Instructions

1. Create a WordPress site that uses block theme, select a style with easily recognizable foreground and background colors (i.e., not black and white).
2. Add the site to the WordPress/Jetpack app.
3. Navigate to Me → Debug settings and enable the following feature flags:
   • experimental_block_editor
   • experimental_block_editor_theme_styles
4. Open the editor for the site.
5. Verify the selected theme styles display.
6. Close the editor.
7. Disable the experimental_block_editor_theme_styles flag.
8. Open the editor for the site.
9. Verify the default styles display.

Regression Notes

1. Potential unintended areas of impact The existing editor fails.
2. What I did to test those areas of impact (or what existing automated tests I relied on) Briefly tested the existing editor.
3. What automated tests I added (or what prevented me from doing so) N/A for this experimental feature.

PR Submission Checklist:

• [x] I have completed the Regression Notes.
• [x] I have considered adding accessibility improvements for my changes.
• [x] I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

Testing Checklist (strike-out the not-applying and unnecessary ones):

• [ ] WordPress.com sites and self-hosted Jetpack sites.
• [ ] Portrait and landscape orientations.
• [ ] Light and dark modes.
• [ ] Fonts: Larger, smaller and bold text.
• [ ] High contrast.
• [ ] Talkback.
• [ ] Languages with large words or with letters/accents not frequently used in English.
• [ ] Right-to-left languages. (Even if translation isn’t complete, formatting should still respect the right-to-left layout)
• [ ] Large and small screen sizes. (Tablet and smaller phones)
• [ ] Multi-tasking: Split screen and Pop-up view. (Android 10 or higher)

[dangermattic]

	1 Message
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[wpmobilebot]

📲 You can test the changes from this Pull Request in WordPress by scanning the QR code below to install the corresponding build.

	App Name	WordPress
	Flavor	Jalapeno
	Build Type	Debug
	Version	pr21324-826ea23
	Commit	826ea2300a6dc63ba3e26265c70e1a5553513597
	Direct Download	wordpress-prototype-build-pr21324-826ea23.apk

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[wpmobilebot]

📲 You can test the changes from this Pull Request in Jetpack by scanning the QR code below to install the corresponding build.

	App Name	Jetpack
	Flavor	Jalapeno
	Build Type	Debug
	Version	pr21324-826ea23
	Commit	826ea2300a6dc63ba3e26265c70e1a5553513597
	Direct Download	jetpack-prototype-build-pr21324-826ea23.apk

Note: Google Login is not supported on these builds.

[sonarcloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 40.23%. Comparing base (5d09cff) to head (826ea23). Report is 10265 commits behind head on trunk.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## trunk #21324 +/- ## ======================================= Coverage 40.23% 40.23% ======================================= Files 1536 1537 +1 Lines 70252 70256 +4 Branches 11543 11543 ======================================= + Hits 28263 28267 +4 Misses 39542 39542 Partials 2447 2447 ```

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[nbradbury]

@dcalhoun Do you have a site I can use to test this? Also, I'm not sure from the description what I should expect to see. Perhaps a video would help?

[dcalhoun]

@dcalhoun Do you have a site I can use to test this? Also, I'm not sure from the description what I should expect to see. Perhaps a video would help?

WordPress.com's Choose a Theme’s Style should provide additional context. The block editor should render content using a theme's styles—i.e., what-you-see-is-what-you-get. You can observe this same feature in the web editor, where the block editor's background color will match your theme's background color, the block editor's text color will match your theme's text color, etc.

An Atomic or jurassic.ninja site should allow for selecting a theme style. Happy to invite you to one of my testing sites, if that is preferred. Just let me know.

[nbradbury]

The block editor should render content using a theme's styles—i.e., what-you-see-is-what-you-get. You can observe this same feature in the web editor, where the block editor's background color will match your theme's background color, the block editor's text color will match your theme's text color, etc.

Thanks for the context. I thought I needed to use a specific block-related theme for this, but I see otherwise. I'll get back to reviewing this.