Backport from core: Global styles duotone not rendering in post editor

[ajlende]

Description

Backport the changes from changeset/52768. As part of the 5.9.1-RC1 release, these changes were made to core.

In addition, since core is loading the global duotone SVG filters, they can be skipped in the plugin if running with WP 5.9.1 or later.

Testing

Using wordpress-develop 5.9.0 and 5.9.1-RC1.

Using a theme that uses global duotone styles such as Skatepark or Twenty Twenty-Two with the following added to the theme.json

{
    "styles": {
        "blocks": {
            "core/image": {
                "filter": {
                    "duotone": "var(--wp--preset--duotone--primary-and-secondary)"
                }
            }
        }
    }
}

Check that the global duotones are applied to images in the post editor without manually adding them via the block interface. And check that there are no duplicate SVGs generated (ex. #wp-duotone-dark-grayscale).

Screenshots

[ajlende]

I see an issue that the SVGs are getting generated at the bottom of the body when testing against 5.9.0. I will look at that tomorrow, but until then, the rest can still be tested.

[oandregal]

The code is the same as in core, so this can go in.

The function name is not a blocker, just a convention we follow. The other one we should address as a follow-up and port to 5.9.1 as well.

[hellofromtonya]

Sorry for my tardiness in reviewing. LGTM 👍

Thanks @ajlende for porting these changes back to this repo ⭐