Add: Template types to the patterns API.

Backports https://github.com/WordPress/gutenberg/pull/45814 into the core.
This commit adds a new templateType property to the patterns registration API.
This property allows a pattern to specify which template it makes sense on, e.g.: 404, single-post, single-product, category.

Props youknowriad, ntsekouras, 
spacedmonkey.
Built from https://develop.svn.wordpress.org/trunk@55168


git-svn-id: http://core.svn.wordpress.org/trunk@54701 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/rest-api/endpoints/class-wp-rest-block-patterns-controller.php

@@ -173,6 +173,7 @@ class WP_REST_Block_Patterns_Controller extends WP_REST_Controller {
 			'keywords'      => 'keywords',
 			'content'       => 'content',
 			'inserter'      => 'inserter',
+			'templateTypes' => 'template_types',
 		);
 		$data   = array();
 		foreach ( $keys as $item_key => $rest_key ) {
@@ -248,6 +249,12 @@ class WP_REST_Block_Patterns_Controller extends WP_REST_Controller {
 					'readonly'    => true,
 					'context'     => array( 'view', 'edit', 'embed' ),
 				),
+				'template_types' => array(
+					'description' => __( 'An array of template types where the pattern fits.' ),
+					'type'        => 'array',
+					'readonly'    => true,
+					'context'     => array( 'view', 'edit', 'embed' ),
+				),
 				'content'        => array(
 					'description' => __( 'The pattern content.' ),
 					'type'        => 'string',