Changeset 52069 for trunk/src/wp-includes/blocks/navigation-area.php

Add Site Editor and PHP changes from Gutenberg 10.1 - 11.9

• First pass at adding the site editor from the Gutenberg plugin to wp-admin/site-editor.php.
• Adds miscellaneous PHP changes from Gutenberg 10.1 - 11.9.

Follows [52042].
See #54337.
Props youknowriad, aristath, hellofromtonya, gziolo.