Theme Export: Restore appearanceTools when exporting a theme

[scruffian]

What?

When you export a theme that declares support for appearanceTools in theme.json we should keep this declaration rather than converting it to the properties that this maps to. Fixes #39464.

Why?

This will make it easier for theme developers to use the theme export tool, and also enable them to easy opt in to more settings in the future.

How?

By overloading the do_opt_in_into_settings method in WP_Theme_JSON_Gutenberg and creating a new one called do_opt_out_of_settings which does the reverse.

Testing Instructions

• Switch to a theme that uses the appearanceTools property in theme.json (e.g. TT2)
• Go to the Site Editor and export the theme
• Confirm that the appearanceTools remain in the theme.json file under settings
• Confirm that the other properties aren't declared:

settings.border.color
settings.border.radius
settings.border.style
settings.border.width
settings.color.link
settings.spacing.padding
settings.spacing.blockGap
settings.spacing.margin

Notes

There are also some other settings that are opted in to (e.g. settings.color.custom, settings.color.customGradient) but this has a different cause so we should look at it in a different PR...

cc @WordPress/block-themers

[scruffian]

This is really hard to read because of the $path[ 0 ] thing, but I'm not sure what would be a better approach...

[adamziel]

Maybe something like

foreach ( static::TO_OPT_IN as list( $group, $prop ) ) {
	if ( ! empty( $theme_json['settings'][ $group ][ $prop ] ) ) {

[draganescu]

Why overload do_opt_in_into_settings?

[scruffian]

Why overload do_opt_in_into_settings?

So that it can use the new class variable - the old one just has that array hardcoded into the function.

[adamziel]

Can unset prop be, or ever become, a valid value? I know it's unlikely for, say, color – but still. How about an object? It should also have a unique identity.

[oandregal]

All existing opt-ins are booleans (or null).

[oandregal]

I was looking into this and thought I'd push a couple of changes to:

• add unit tests
• implement the behavior for both top-level and block-level settings

[scruffian]

Thanks @oandregal. I fixed a few linting issues...