Editor: Ignore theme.json values of unexpected types

[ramonjd]

Trac ticket: https://core.trac.wordpress.org/ticket/66286

Backports WordPress/gutenberg#84523.

What

Stops WP_Theme_JSON from throwing fatal TypeErrors when theme.json or global styles data contains values of the wrong type.

Why

The Gutenberg report came from a live site where every front-end page fatalled:

PHP Fatal error: Uncaught TypeError: explode(): Argument #2 ($string) must be of type string, array given
#1 WP_Theme_JSON_Gutenberg::process_blocks_custom_css(Array, 'a:where(:not(.w...')
#2 WP_Theme_JSON_Gutenberg->get_styles_for_block(Array)

sanitize() keeps schema leaves such as css and spacingScale whatever their type, so an array css value reaches explode() in process_blocks_custom_css(). The same gap fatals in a few other places.

What changed

Values of unexpected types are now ignored instead of crashing:

• css that isn't a string produces no output (the reported crash).
• ref that isn't a string is ignored.
• A spacingScale that isn't an array, or a spacingScale.unit that isn't a string, is ignored.
• Shared block style variations that aren't arrays, and blockTypes items that aren't strings, are skipped.

Valid data is unaffected.

Each case has a test. All nine new cases fail on trunk with a TypeError.

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[github-actions]

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