Theme JSON: Fix handling of default presets at block level

[aaronrobertshaw]

Trac ticket: https://core.trac.wordpress.org/ticket/64195

This PR brings the changes from the following Gutenberg PRs to core:

WordPress/gutenberg#72916

Description

Prevents an issue where block level presets do not work correctly when:

• Default presets are disabled
• Slug matches the default preset

The result is missing presets in the settings and editor UI.

Testing

For each theme.json example config below:

1. Ensure default presets for the feature being testing is on at the global level
2. Add the block level preset config to your theme.json file
3. Confirm in the editor the expected presets are available generally and at the block level

Duotone

In the image block, only the "Dark grayscale" duotone preset should be available

{
	"version": 3,
	"appearanceTools": true,
	"settings": {
		"blocks":{
			"core/image": {
				"color": {
					"defaultDuotone": false,
					"duotone": [
						{
							"name": "Dark grayscale",
							"colors": [ "#000000", "#7f7f7f" ],
							"slug": "dark-grayscale"
						}
					]
				}
			}
		}
	}
}

Shadow

In the image block, only the "Natural" shadow preset should be available

{
	"version": 3,
	"settings": {
		"appearanceTools": true,
		"blocks":{
			"core/image": {
				"shadow": {
					"defaultPresets": false,
					"presets": [
						{
							"name": "Natural",
							"slug": "natural",
							"shadow": "6px 6px 9px rgba(0, 0, 0, 0.2)"
						}
					]
				}
			}
		}
	}
}

Font Size

In the Paragraph block, only the "Small" duotone preset should be available

{
	"version": 3,
	"settings": {
		"appearanceTools": true,
		"blocks":{
			"core/paragraph": {
				"typography": {
					"defaultFontSizes": false,
					"fontSizes": [
						{
							"name": "Small",
							"slug": "small",
							"size": "13px"
						}
					]
				}
			}
		}
	}
}

Screenshots or screencast

Before	After

---

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[github-actions]

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[ramonjd]

LGTM

Tested in the same way as WordPress/gutenberg#72916