What problem does this address?

As implemented previously, when registering patterns with 'blockTypes' => array( 'core/post-content' ) annotation, they appear in a modal when creating a new page:

The small modal becomes unwieldly very quickly when a theme or plugin registers dozens of patterns:

What is your proposed solution?

• Add possibility to add categories.
• Increase the modal size to (almost) full browser size to accommodate categories and, be able to see patterns better
• Add search input. When it makes sense to add lots of patterns, it makes sense to let search them, too.

Basically re-use already existing "Explore all patterns" modal. That seemed to be intention in the original issue as well.

Categories could be pulled from existing categories key, without needing to introduce new APIs.