Scaffold new block directory structure and build process

[jaymcp]

We are migrating our custom blocks to v3 of the Block API to better support modern WordPress features.

To make block management easier, we should migrate away from our custom Webpack build process, and adopt wp-scripts.

To minimise the amount of configuration required, and to future-proof our blocks, we should adopt the default directory structure.

Currently, our blocks have code in several places:

• /private/src/scripts/editor/blocks contains our JS block registration, display components, and (in some cases) save components
• /private/src/scripts/modules contains frontend interactivity JS modules
• /private/src/styles/blocks contains our SCSS
• /wp-content/themes/humanity-theme/includes/blocks contains our PHP block registration and server-side block renderer functions

This is unwieldy, and makes block management frustrating. The new directory structure is greatly simplified:

• source/blocks contains everything!

Each block should have its own directory within source/blocks, and should contain the following files (where applicable):

• block.json - this contains the block metadata (attributes, name, description, etc)
• edit.js - the display component(s)
• view.js - any frontend interactivity
• render.php - server side-rendered markup
• editor.scss - styles for the block editor
• style.scss - styles for the site editor / frontend
• index.js - block registration
• save.js - block save component