Do not SSR in legacy themes

[nateconley]

Description of the Change

Disallows legacy themes from server side render in the block editor. These older themes do not have the full stylesheet enabled in the block editor and will instead apply core's forms.css for admin forms.

Closes #2

How to test the Change

• Form is rendered in the block editor for Twenty Twenty-Four when not focuses.
• Form does not render in the block editor for Twenty Twenty-One

Changelog Entry

Enhances: new block

Credits

@nateconley

Checklist:

• [x] I agree to follow this project's Code of Conduct.
• [ ] I have updated the documentation accordingly.
• [ ] I have added tests to cover my change.
• [x] All new and existing tests pass.

[nateconley]

@dkotter To address your concerns on Twenty Twenty-Four, here is what Contact Form 7 looks like:

I think the best path forward here might be to add field "Padding" and "Button" settings to the "Custom Styling" section - I can add that in.

For the denylist, I think this is going to be difficult to accomplish consistently, as we really don't have a reliable way to figure out how much of the theme style is added to the editor.

[dkotter]

@nateconley Sorry, just saw your message as I was working on this. I've added in some basic padding to all form elements and things look much better to me now with the ability to still easily override that on a theme level:

Though feel free to adjust further if needed

[nateconley]

@dkotter If this is working well across themes, I think this is a great path forward. Thanks!

[nateconley]

@dkotter I gave this a quick look in themes 2024, 2023, 2022, and 2021 and it looks great!