theme.json schema: Update appearanceTools description

[t-hamano]

What?

This PR adds the missing setting in the theme.json schema that settings.apperanceTools actually enables:

• color.heading
• color.button
• color.caption
• shadow.defaultPresets

How?

Referenced APPEARANCE_TOOLS_OPT_INS variable and added missing settings.

Testing Instructions

Create a JSON file like below locally and make sure settings.apperanceTools displays the correct description text.

{
	"$schema": "https://raw.githubusercontent.com/WordPress/gutenberg/theme-json/update-appearance-tools/schemas/json/theme.json",
	"version": 2,
	"settings": {
		"appearanceTools": false
	}
}

Screenshots or screencast

Before

After

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[fabiankaegy]

Good catch :)

[andrewserong]

Thanks for updating!

[madhusudhand]

Thank you for taking care of this.