Fix: Block style variations containing ref values

[aaronrobertshaw]

This ticket tracks the backporting of PHP files for the following Gutenberg updates:

• ​https://github.com/WordPress/gutenberg/pull/63172

These changes fix an issue where block style variations that use ref values to reference styles elsewhere in theme.json weren't working.

This PR backports the fix from:

• ​https://github.com/WordPress/gutenberg/pull/63172

This restores the ability to reference style values from elsewhere within theme.json for block style variations.

Trac ticket: https://core.trac.wordpress.org/ticket/61589#ticket

#### Test Instructions

1. Add some ref values for block style variations to your theme.json e.g. update TT4 with the sections from the theme.json snippet below
2. Load the site editor and edit the default home page
3. Confirm that outline buttons are displayed and have the correct referenced style values
4. Save and ensure the same on the frontend

<details>
<summary>Example theme.json snippet</summary>

{
    "styles": {
        "elements": {
            "button": {
                "border": {
                    "color": "transparent",
                    "radius": "0.25em",
                    "style": "solid",
                    "width": "1px"
                },
                "color": {
                    "background": "var(--wp--preset--color--accent)",
                    "text": "var(--wp--preset--color--base)"
                },
                "spacing": {
                    "padding": {
                        "bottom": "0.5em",
                        "left": "1.25em",
                        "right": "1.25em",
                        "top": "0.5em"
                    }
                }
            }
        },
        "blocks": {
            "core/button": {
                "border": {
                    "color": { "ref": "styles.elements.button.border.color" },
                    "radius": { "ref": "styles.elements.button.border.radius" },
                    "style": { "ref": "styles.elements.button.border.style" },
                    "width": { "ref": "styles.elements.button.border.width" }
                },
                "color": {
                    "background": { "ref": "styles.elements.button.color.background" },
                    "text": { "ref": "styles.elements.button.color.text" }
                },
                "spacing": {
                    "padding": {
                        "bottom": { "ref": "styles.elements.button.spacing.padding.bottom" },
                        "left": { "ref": "styles.elements.button.spacing.padding.left" },
                        "right": { "ref": "styles.elements.button.spacing.padding.right" },
                        "top": { "ref": "styles.elements.button.spacing.padding.top" }
                    }
                },
                "variations": {
                    "outline": {
                        "border": {
                            "color": "currentColor",
                            "width": { "ref": "styles.elements.button.border.width" }
                        },
                        "color": {
                            "text": { "ref": "styles.elements.button.color.background" }
                        },
                        "spacing": {
                            "padding": {
                                "bottom": { "ref": "styles.elements.button.spacing.padding.bottom" },
                                "left": { "ref": "styles.elements.button.spacing.padding.left" },
                                "right": { "ref": "styles.elements.button.spacing.padding.right" },
                                "top": { "ref": "styles.elements.button.spacing.padding.top" },
                            }
                        }
                    }
                }
            }
        }
    }
}

</details>

## Screenshots or screencast

Before	After

[ellatrix]

In 58690:

Section Styles: Prevent flash of variation style updates.

This is fixed by preloading the styles.

Fixes #61589.
Fixes ​https://github.com/WordPress/wordpress-develop/pull/6989.
See ​https://github.com/WordPress/gutenberg/pull/63172.

Props aaronrobertshaw, andrewserong, ramonopoly.

[ellatrix]

Apologies, I got confused between the tickets. [58690] fixed #61553, not this ticket.

[ellatrix]

In 58691:

Section Styles: Fix ref values within block style variations.

Fixes #61589.
Fixes ​https://github.com/WordPress/wordpress-develop/pull/6989.
See ​https://github.com/WordPress/gutenberg/pull/63172.

Props aaronrobertshaw, andrewserong, ramonopoly.

[audrasjb]

This changeset looks good to me. This is a second committer sign-off. Marking as dev-reviewed.

[hellofromTonya]

In 58699:

Editor: Fix ref values within block style variations.

Fixes an issue where block style variations that use ref values to reference styles elsewhere in theme.json weren't working.

Retrieves reference values when generating styles for block style variations. How? When retrieving variation data, to generate styles from, also retrieve any referenced values.

Reviewed by audrasjb.
Merges [58691] to the 6.6 branch.

Props aaronrobertshaw, andrewserong, ramonopoly.
Fixes #61589.