gutenberg_register_packages_scripts() can only be run once

[mdawaffe]

Describe the bug

If gutenberg_register_packages_scripts() is run more than once, the dependencies for any packages' scripts with a core handle are removed.

The require_once() call will return true on all but the first run of gutenberg_register_packages_scripts(), which will wipe out any dependencies.

gutenberg/lib/client-assets.php

Lines 240 to 243 in 6fc0b70

	$asset = file_exists( $asset_file )
	? require_once( $asset_file )
	: null;
	$dependencies = isset( $asset['dependencies'] ) ? $asset['dependencies'] : array();

Introduced in #17298.

To reproduce
Steps to reproduce the behavior:

1. Install an mu-plugin:

   <?php
   
   add_action( 'after_setup_theme', function() {
           wp_enqueue_script( 'jquery' );
   } );
   
   add_action( 'init', function() {
           wp_enqueue_script( 'wp-a11y' );
   } );

2. Go to the homepage.
3. See the following error in the JS Console:

   Uncaught TypeError: o(...) is not a function
      at Module.321 (index.js?ver=1574117808:1)
      at n (index.js?ver=1574117808:1)
      at wp.a11y.186 (index.js?ver=1574117808:1)
      at index.js?ver=1574117808:1
   

4. View the homepage's HTML source.
5. See that a11y has been included, but not dom-ready.

Expected behavior

gutenberg_register_packages_scripts() should be able to be run more than once.

Additional context

• Gutenberg 6.9.0