Taxonomies: Load all taxonomies

[youknowriad]

closes #9589

By default the REST API requests load a limited chunk of records (pagination). This PR makes sure we load all the taxonomies.

Testing instructions

Register a bunch of taxonomies and test that they appear all.

add_action( 'init', 'loadtaxonomies' );

function loadtaxonomies() {
for ( $i = 1; $i <20; $i++) {
   register_taxonomy(
   	'genre'. $i,
   	'post',
   	array(
   		'label' => __( 'Genre' ),
   		'rewrite' => array( 'slug' => 'genre' ),
   		'hierarchical' => true,
   		'show_in_rest' => true
   	)
   );
}
}

[tofumatt]

An E2E test for this might be handy, but code makes sense.

Tested locally and it works 👍

[danielbachhuber]

By default the REST API requests load a limited chunk of records (pagination). This PR makes sure we load all the taxonomies.

Notably, the REST API itself doesn't use a per_page argument for /wp/v2/taxonomies. There's no pagination on that endpoint.

On the other endpoints that support pagination, the default is per_page=10 so I'm not sure where the magic 8 number is coming from the original bug report.

Also, on master, I notice there's still a wp/v2/taxonomies?context=edit request still being made: