Premium Content: Tidy up deprecation errors.

[kwight]

Starting with WordPress/gutenberg#22686, the PHP register_block_type block arguments for context and providesContext were deprecated (replaced by uses_context and provides_context respectively). This PR updates the usage to quiet the doing_it_wrong() errors.

Testing Instructions

• Set up a JN test site that is connected to WP.com and has a JP Premium plan attached.
• Install the latest Gutenberg plugin.
• Use the build artifact from the FSE plugin / Build FSE plugin (pull_request) task below as a ZIP plugin that you can upload to the test site.
• Create a post, and add a Premium Content block for testing.
• Save the post, and check the front-end of the post: the above errors should not display.

[matticbot]

Test live: https://calypso.live/?branch=fix/premium-content-deprecations

[matticbot]

Caution: This PR affects files in the FSE Plugin on WordPress.com
Please ensure your changes work on WordPress.com before merging.

D46453-code has been created so you can easily test it on your sandbox. See this FieldGuide page about developing in the FSE Plugin for more info: PCYsg-ly5-p2

[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.

[blackjackkent]

Tested this in JN and am seeing a PHP error when viewing the Premium Content widget as a subscriber - however, it's a different error than the one in your screenshot:

Deprecated: Non-static method Automattic\Jetpack\Connection\Manager::get_access_token() should not be called statically in /srv/users/user824aad5a/apps/user824aad5a/public/wp-content/plugins/fse-build-archive/premium-content/subscription-service/class-jetpack-token-subscription-service.php on line 35

I'm not sure if this is directly connected to your fix or not.

[gwwar]

You're right, @blackjackkent it looks like we have other warnings to tidy, but we can fix those in follow up PRs.

@kwight I verified that the context warnings no longer appear in Gutenberg 8.3 and 8.5.1