Block Editor: Add preloading of autosaves.

With the introduction of WordPress/gutenberg#7945, the block editor requests autosave data when the editor is loaded. This can be optimized by preloading the request server-side and then passing the request data to the client using the preloading mechanism in editor-form-blocks.php.

Props: talldanwp, aduth.
Built from https://develop.svn.wordpress.org/trunk@46110


git-svn-id: https://core.svn.wordpress.org/trunk@45922 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/edit-form-blocks.php

@@ -49,6 +49,7 @@
 	sprintf( '/wp/v2/users/me?post_type=%s&context=edit', $post_type ),
 	array( '/wp/v2/media', 'OPTIONS' ),
 	array( '/wp/v2/blocks', 'OPTIONS' ),
+	sprintf( '/wp/v2/%s/%d/autosaves?context=edit', $rest_base, $post->ID ),
 );
 
 /**

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.3-alpha-46109';
+$wp_version = '5.3-alpha-46110';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.