Add origin and author to template rest api

[talldan]

Description

This replicates the changes to the core REST API proposed by WordPress/wordpress-develop#1937 for Gutenberg.

related UI changes - #36763

[spacedmonkey]

Can we update the schema tests to ensure these new properties are found in the REST API.

[talldan]

Can we update the schema tests to ensure these new properties are found in the REST API.

I had a look into this, but it doesn't seem possible right now because the Gutenberg version of the REST API uses some code from WordPress core, which doesn't contain the necessary changes just yet.

Some examples:

• gutenberg/lib/load.php

  Lines 103 to 105 in df38b3d

  	if ( ! class_exists( 'WP_Block_Template' ) ) {
  	require __DIR__ . '/full-site-editing/class-wp-block-template.php';
  	}

• gutenberg/lib/compat/wordpress-5.9/block-template-utils.php

  Line 533 in df38b3d

  if ( ! function_exists( '_build_block_template_result_from_post' ) ) {

I don't think the way it's working in the plugin is quite right, I already noticed that the Gutenberg version of the REST API is still active when running 5.9 as an example - #36898.

I'll follow up to fix these things.

[talldan]

I had a look into this, but it doesn't seem possible right now because the Gutenberg version of the REST API uses some code from WordPress core, which doesn't contain the necessary changes just yet.

Looks like I did need to update the tests. I don't think it's possible to test author support fully though until _build_block_template_result_from_post supports it in core.