Add CSS Custom Property for layout width to editor and frontend

[fabiankaegy]

Description

Pretty much all the options that we set in theme.json are available to theme & plugin authors via CSS Custom Properties. That is not the case for the layout width settings.

It would be really useful to be able to access the contentWidth and wideWidth values as custom properties.

{
  "version": 1,
  "settings": {
    "layout": {
      "contentSize": "800px",
      "wideSize": "1000px"
    }
  }
}

Based on the other properties the naming scheme would probably be something like:

--wp--preset--layout--content-size: 800px;
--wp--preset--layout--wide-size: 1000px;

Step-by-step reproduction instructions

does not apply

Screenshots, screen recording, code snippet

No response

Environment info

No response

Please confirm that you have searched existing issues in the repo.

Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

Yes

[chthonic-ds]

See #30081.

[fabiankaegy]

Thanks for raising that ticket :) Closing in favor of #30081.