Editor: Add is block theme setting to get_block_editor_settings().

The block editor's iframe needs to know if the theme is a block theme. This changeset adds a setting to `get_block_editor_settings()`.

Reference:
* https://github.com/WordPress/gutenberg/pull/46212

Props ellatrix, alexstine, costdev, dgwyer, glendaviesnz, scruffian.
Fixes #57549.
Built from https://develop.svn.wordpress.org/trunk@55147


git-svn-id: http://core.svn.wordpress.org/trunk@54680 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/block-editor.php

@@ -495,6 +495,7 @@ function get_block_editor_settings( array $custom_settings, $block_editor_contex
 	}
 
 	$editor_settings['__unstableResolvedAssets']         = _wp_get_iframed_editor_assets();
+	$editor_settings['__unstableIsBlockBasedTheme']      = wp_is_block_theme();
 	$editor_settings['localAutosaveInterval']            = 15;
 	$editor_settings['disableLayoutStyles']              = current_theme_supports( 'disable-layout-styles' );
 	$editor_settings['__experimentalDiscussionSettings'] = array(

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.2-alpha-55146';
+$wp_version = '6.2-alpha-55147';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.