Plugin: Seek to eliminate or substitute packages for globals references

[aduth]

Related: #14837 (comment)
Meeting discussion (link requires registration): https://wordpress.slack.com/archives/C5UNMSU4R/p1556028118143500

There are multiple occurrences of window globals being referenced in code. These are incompatible for use in an npm context and should be eliminated or substituted with an equivalent package.

From https://wordpress.slack.com/archives/C5UNMSU4R/p1556030096195300 :

there are 4 packages only: postbox, media-views, editor and media-models

From https://wordpress.slack.com/archives/C5UNMSU4R/p1556030164197100 :

existing packages which depend on them are block-library and edit-post

[gziolo]

I identified those indirect dependencies manually by scanning packages-dependencies.php file:

wp-block-library:

gutenberg/lib/packages-dependencies.php

Line 25 in 354c1ff

'editor',

gutenberg/packages/block-library/src/index.js

Line 99 in 354c1ff

window.wp && window.wp.oldEditor ? classic : null, // Only add the classic block in WP Context

wp-edit-post:

gutenberg/lib/packages-dependencies.php

Lines 133 to 135 in 354c1ff

	'postbox',
	'media-models',
	'media-views',

[gziolo]

This is how @sirreal implemented the handling of indirect dependencies in #15124:

gutenberg/lib/client-assets.php

Lines 197 to 206 in 6de12cc

	// Add dependencies that cannot be detected and generated by build tools.
	switch ( $handle ) {
	case 'wp-block-library':
	array_push( $dependencies, 'editor' );
	break;
	case 'wp-edit-post':
	array_push( $dependencies, 'media-models', 'media-views', 'postbox' );
	break;
	}