Initial commit for the new gallery block

[dgwyer]

This PR includes the new gallery block which uses a modern structure and tooling, based on the @wordpress.create-block script.

As this PR introduces new npm packages and removes others it's recommended to do an npm ci. If that doesn't work then delete the node_modules folder and package.json and run npm i. I'm using Node version 16.18.0.

Build files are included in the commit so there is no need to compile the block source before testing. But if you want to build then either run npm start to build/watch or just npm run build to build.

To test just add a gallery block to a page and check it displays ok on the frontend and in the editor.

[dgwyer]

@giucu91 I noticed the tests failed after submitting the PR. Can you let me know the status of the tests on this repo. i.e. Is it something in the PR causing them to fail or a more general issue?

[razvanaldea89]

When going through the present galleries something weird happens to the select: it multiplies or something.

Also, on the first attempt of saving a page with the new block a JSON error appeared. After a few tries it went away and never happened.

Update: Seems to be happening ( the duplication ) if a gallery doesn't have images.

[dgwyer]

Thanks for testing. 😊

I just tried the 2.7.5 branch and the duplication issue is happening there, so it's not specific to this PR I don't think.

And would you mind elaborating on the JSON issue? What was the issue exaclty that you saw, and are the steps replicable?

Also, on the first attempt of saving a page with the new block a JSON error appeared. After a few tries it went away and never happened.