Bundle the WP_Theme_JSON_Resolver class as a single file instead of…

… inheriting per WordPress version (#46750)

* Backport WP_Theme_JSON_Resolver from core as it is

* Substitute WP_Theme_JSON by WP_Theme_JSON_Gutenberg

* Substitute WP_Theme_JSON_Data by WP_Theme_JSON_Data_Gutenberg

* Rename WP_Theme_JSON_Resolver to WP_Theme_JSON_Resolver_Base

The goal is to use it as base to inherit from, until we are able
to remove all the children.

* Make WP_Theme_JSON_Resolver_6_1 inherit from WP_Theme_JSON_Resolver_Base

* 6.1: remove field already defined in base class

* 6.1: remove translate, it is equal to base method

* 6.1: remove get_core_data, it does not have base changes

* 6.1: remove get_user_data

Missed core changes and does not do anything differently from core.

* 6.1: remove get_user_data_from_wp_global_styles

It misses core changes and does not do anything differently.

* 6.2: inherit from WP_Theme_JSON_Resolver_Base instead of 6.1

This makes the WP_Theme_JSON_Resover_6_1 class unused.

* 6.1: remove class no longer in use

* 6.2: deprecate theme_has_support

#45380

* 6.2: substitute WP_Theme_JSON_Resolver::theme_has_support

by wp_theme_has_theme_json()

#45168

* 6.2: port changes to get_user_data_from_wp_global_styles

#46043

* 6.2: update get_merged_data

#45969

* 6.2: remove get_user_data

Same code as core. There's a check for detecting whether the class
is an instance of WP_Theme_JSON_Gutenberg that was not ported.
This check was introduced to make sure the cache of the core class
didn't interfere with the cache of the Gutenberg class,
so it's no longer necessary.

See #42756

* experimental: make it inherit from WP_Theme_JSON_Resolver_Base

* 6.2: remove class no longer in use

* experimental: delete remove_json_comments

It's already part of the base class.

* experimental: remove get_block_data

It's already part of the base class and it didn't have
the changes from core.

* experimental: appearanceTools

Port changes to the base class that were meant to be part of 6.1.
See #43337

* experimental: port webfonts (experimental API)

see #37140

* experimental: use gutenberg_get_legacy_theme_supports_for_theme_json

#46112

* experimental: get_theme_data, all code is in the base class

* experimental: remove empty class

* Rename WP_Theme_JSON_Resolver_Base to WP_Theme_JSON_Resolver_Gutenberg

* Fix lint issue: rename class-wp-theme-json-resolver.php to class-wp-theme-json-resolver-gutenberg.php

* Move theme.json to unversioned lib/

* Move theme-i18n.json to unversioned lib/