Editor: Add explicit template and template_lock attributes

Add and document the template and template_lock attributes on WP_Post_Type that
are used by the block editor.

Props metalandcoffee.
See #46261.


git-svn-id: https://develop.svn.wordpress.org/trunk@49492 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/class-wp-post-type.php

@@ -260,6 +260,37 @@ final class WP_Post_Type {
 	 */
 	public $delete_with_user = null;
 
+	/**
+	 * Array of blocks to use as the default initial state for an editor
+	 * session. Each item should be an array containing block name and
+	 * optional attributes.
+	 *
+	 * Default empty array.
+	 *
+	 * @link https://developer.wordpress.org/block-editor/developers/block-api/block-templates/
+	 *
+	 * @since 5.6.0
+	 * @var array $template
+	 */
+	public $template = array();
+
+	/**
+	 * Whether the block template should be locked if $template is set.
+	 *
+	 * If set to 'all', the user is unable to insert new blocks, move existing blocks
+	 * and delete blocks.
+	 * If set to 'insert', the user is able to move existing blocks but is unable to insert
+	 * new blocks and delete blocks.
+	 *
+	 * Default false.
+	 *
+	 * @link https://developer.wordpress.org/block-editor/developers/block-api/block-templates/
+	 *
+	 * @since 5.6.0
+	 * @var string|bool $template_lock
+	 */
+	public $template_lock = false;
+
 	/**
 	 * Whether this post type is a native or "built-in" post_type.
 	 *
@@ -415,6 +446,8 @@ final class WP_Post_Type {
 			'show_in_rest'          => false,
 			'rest_base'             => false,
 			'rest_controller_class' => false,
+			'template'              => array(),
+			'template_lock'         => false,
 			'_builtin'              => false,
 			'_edit_link'            => 'post.php?post=%d',
 		);