Make post title contextual and translatable

This just uses the stock WordPress objects.

gutenberg.php

@@ -27,10 +27,12 @@
  * @since 0.1.0
  */
 function the_gutenberg_project() {
+	global $post_type, $post_type_object;
+	$post_type_object = get_post_type_object( $post_type );
 	?>
 	<div class="nvda-temp-fix screen-reader-text">&nbsp;</div>
 	<div class="gutenberg">
-		<h1 class="screen-reader-text">Edit Post</h1>
+		<h1 class="screen-reader-text"><?php echo esc_html( $post_type_object->labels->edit_item ); ?></h1>
 		<div id="editor" class="gutenberg__editor"></div>
 		<div id="metaboxes" style="display: none;">
 			<?php the_gutenberg_metaboxes(); ?>