Deprecate '@wordpress/nux' package #18981
What this does:
How to test:
The welcome guide should not appear and the sidebar should still be closed.
SPT is currently dispatching a `disableTips` action for disabling the welcome guide when the page layout selector is displayed, but `@wordpress/nux` will be deprecated and not imported by default in Gutenberg 7.2.0 (WordPress/gutenberg#18981). That means that `disableTips` will not be available and will break the editor: This PR handles that deprecation by hiding the welcome guide using `isFeatureActive( 'welcomeGuide' )`/`toggleFeature( 'welcomeGuide' )` (available since Gutenberg 7.1.0) and defers to `disableTips` only when the action is available (Gutenberg 7.0.0 and below).