Adds `wp_theme_has_theme_json()` for public consumption, to replace the private internal Core-only `WP_Theme_JSON_Resolver::theme_has_support()` method. This new global function checks if a theme or its parent has a `theme.json` file.
For performance, results are cached as an integer `1` or `0` in the `'theme_json'` group with `'wp_theme_has_theme_json'` key. This is a non-persistent cache. Why? To make the derived data from `theme.json` is always fresh from the potential modifications done via hooks that can use dynamic data (modify the stylesheet depending on some option, settings depending on user permissions, etc.).
Also adds a new public function `wp_clean_theme_json_cache()` to clear the cache on `'switch_theme'` and `start_previewing_theme'`.
References:
* [https://github.com/WordPress/gutenberg/pull/45168 Gutenberg PR 45168] Add `wp_theme_has_theme_json` as a public API to know whether a theme has a `theme.json`.
* [https://github.com/WordPress/gutenberg/pull/45380 Gutenberg PR 45380] Deprecate `WP_Theme_JSON_Resolver:theme_has_support()`.
* [https://github.com/WordPress/gutenberg/pull/46150 Gutenberg PR 46150] Make `theme.json` object caches non-persistent.
* [https://github.com/WordPress/gutenberg/pull/45979 Gutenberg PR 45979] Don't check if constants set by `wp_initial_constants()` are defined.
* [https://github.com/WordPress/gutenberg/pull/45950 Gutenberg PR 45950] Cleaner logic in `wp_theme_has_theme_json`.
Follow-up to [54493], [53282], [52744], [52049], [50959].
Props oandregal, afragen, alexstine, aristath, azaozz, costdev, flixos90, hellofromTonya, mamaduka, mcsf, ocean90, spacedmonkey.
Fixes#56975.
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