Block Editor: Expose value of user_can_richedit().

In order for the Block Editor to know whether to allow visual editing, it needs to know the value of `user_can_richedit()`.

Props youknowriad.
Fixes #45375.


git-svn-id: https://develop.svn.wordpress.org/branches/5.0@43916 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/edit-form-blocks.php

@@ -273,6 +273,7 @@
 	'allowedMimeTypes'       => get_allowed_mime_types(),
 	'styles'                 => $styles,
 	'imageSizes'             => $available_image_sizes,
+	'richEditingEnabled'     => user_can_richedit(),
 	'postLock'               => $lock_details,
 	'postLockUtils'          => array(
 		'nonce'       => wp_create_nonce( 'lock-post_' . $post->ID ),