SPT: Handle NUX deprecation

[mmtr]

Changes proposed in this Pull Request

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).

Testing instructions

• Generate a new build of the FSE plugin and upload it to a WP.org test site.
• Make sure you're running a custom build of the Gutenberg plugin based on master (so the NUX package is deprecated).
• Clear your browser's persisted state by running localStorage.clear() in DevTools.
• Go to Pages > Add New.
• Verify the page layout selector is displayed without the welcome guide.
• Deactivate the Gutenberg plugin (so WP loads the block editor bundled in core where the NUX package is not deprecated yet).
• Clear your browser's persisted state by running localStorage.clear() in DevTools.
• Go to Pages > Add New.
• Verify the page layout selector is displayed without the welcome guide.

[matticbot]

Test live: https://calypso.live/?branch=fix/spt-nux-deprecated

[matticbot]

This PR does not affect the size of JS and CSS bundles shipped to the user's browser.

Generated by performance advisor bot at iscalypsofastyet.com.

[Copons]

@mmtr Once fixed #38611 (comment), this is good to go! 🕺
Thanks for the catch and the fix!

[mmtr]

Thanks for the review @Copons!