Remove reliance upon gutenberg_initialize_editor().

[dd32]

Describe the bug
In WordPress/gutenberg#53527 Gutenberg removed the gutenberg_initialize_editor() method which we use here:

pattern-directory/public_html/wp-content/plugins/pattern-creator/pattern-creator.php

Lines 164 to 172 in 11bccb6

	gutenberg_initialize_editor(
	'block-pattern-creator',
	'pattern-creator',
	array(
	'preload_paths' => array(),
	'initializer_name' => 'initialize',
	'editor_settings' => $settings,
	)
	);

This is causing a fatal error with the Pattern Directory + Gutenberg 16.5.0.

E_ERROR: Uncaught Error: Call to undefined function WordPressdotorg\Pattern_Creator\gutenberg_initialize_editor() in /wp-content/plugins/pattern-creator/pattern-creator.php:164