[Block Library - Query Pagination]: Try rendering hidden element when no next/previous link exists

[ntsekouras]

What?

Attempt to fix: #34997
Alternative of:#40553 and #36681.

I'm still not sure if we want to render an element for design purposes only and I think that the proper approach would be a new layout or some layout controls, that do not exist right now..

We need to weight the pros and cons of such approach and I haven't done all the testing and considered everything yet. But I acknowledge that this is a very common use case that needs to be handled somehow.

I started exploring a layout grid approach, but it needs exploration and if I come up with something good, I'll open a PR for that.

How?

In this PR I render a hidden element only if there was no link for Query Pagination Next/Previous and only if the parent Query Pagination block has justification content center or space-between.

[ntsekouras]

The problem in this PR for now is that if we have no results it will still display the Query Pagination blocks with two visibility:hidden; We could try to add logic to detect this here: https://github.com/WordPress/gutenberg/blob/trunk/packages/block-library/src/query-pagination/index.php#L17 and see how complex it becomes and if it's worth it. If we add similar logic to previous/next blocks the complexity is quite big and has been explored before.

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--edit: I pushed a rough POC to handle the above issue.

[ntsekouras]

Closing in favor of #42764