Build: Improve Gutenberg integration workflow.

This changeset improves the Gutenberg build integration to simplify the developer workflow and reinstore a flow similar to how package dependencies worked before the Gutenberg checkout-and-build approach was introduced.

Key improvements:
* Automatic rebuild on ref change: Adds a new `gutenberg:sync` script that stores a hash of the built ref in `.gutenberg-hash` and only rebuilds when the ref changes.
* Full integration on `npm install`: Running `npm install` now produces a fully working development environment with Gutenberg assets in `src/`.
* Clean Gutenberg checkout: Restores Gutenberg's `package.json` after the build completes.
* Stops copying `.js.map` files to `wp-includes/js/dist` since they reference non-existent paths.
* Remove package.json files from the build folder.
* Avoid closures and use prefixed functions.
* Updates build checks to use `jquery.js` instead of `edit-post.js` as the build indicator.

Props youknowriad, ellatrix, mcsf, dmsnell, ntsekouras, jorgefilipecosta, tobiasbg, peterwilsoncc.
Fixes #64393.

git-svn-id: https://develop.svn.wordpress.org/trunk@61492 602fd350-edb4-49c9-b593-d223f7449a82
(cherry picked from commit e626725)

Author: youknowriad

src/wp-includes/blocks.php

@@ -2421,6 +2421,10 @@ function parse_blocks( $content ) {
 	 */
 	$parser_class = apply_filters( 'block_parser_class', 'WP_Block_Parser' );
 
+	if ( ! class_exists( $parser_class ) ) {
+		return array();
+	}
+
 	$parser = new $parser_class();
 	return $parser->parse( $content );
 }

src/wp-includes/formatting.php

@@ -5227,6 +5227,11 @@ function wp_pre_kses_less_than_callback( $matches ) {
  * @return string Filtered text to run through KSES.
  */
 function wp_pre_kses_block_attributes( $content, $allowed_html, $allowed_protocols ) {
+	// If the block parser isn't available, skip block attribute filtering.
+	if ( ! class_exists( 'WP_Block_Parser' ) ) {
+		return $content;
+	}
+
 	/*
 	 * `filter_block_content` is expected to call `wp_kses`. Temporarily remove
 	 * the filter to avoid recursion.

src/wp-settings.php

@@ -377,9 +377,15 @@
 require ABSPATH . WPINC . '/class-wp-block.php';
 require ABSPATH . WPINC . '/class-wp-block-list.php';
 require ABSPATH . WPINC . '/class-wp-block-metadata-registry.php';
-require ABSPATH . WPINC . '/class-wp-block-parser-block.php';
-require ABSPATH . WPINC . '/class-wp-block-parser-frame.php';
-require ABSPATH . WPINC . '/class-wp-block-parser.php';
+if ( file_exists( ABSPATH . WPINC . '/class-wp-block-parser-block.php' ) ) {
+	require ABSPATH . WPINC . '/class-wp-block-parser-block.php';
+}
+if ( file_exists( ABSPATH . WPINC . '/class-wp-block-parser-frame.php' ) ) {
+	require ABSPATH . WPINC . '/class-wp-block-parser-frame.php';
+}
+if ( file_exists( ABSPATH . WPINC . '/class-wp-block-parser.php' ) ) {
+	require ABSPATH . WPINC . '/class-wp-block-parser.php';
+}
 require ABSPATH . WPINC . '/class-wp-classic-to-block-menu-converter.php';
 require ABSPATH . WPINC . '/class-wp-navigation-fallback.php';
 require ABSPATH . WPINC . '/block-bindings.php';