Feature: Use wp-scripts BBT-37

[g-elwell]

What's changed?

This PR updates the local development setup to utilise @wordpress/scripts in place of the Big Bite build tools.

Fixes BBT-37

This change also allowed us to migrate the remaining WordPress dependencies to module imports rather than relying on accessing the global wp namespace.

Change log:

• Removed @bigbite/build-tools and related npm scripts
• Installed @wordpress/scripts and added relevant npm scripts
• Moved script entrypoint to the default location expected by wp-scripts (/src/index.js)
• Updated asset enqueuing to utilise wp-scripts generated asset files
• Updated wp global imports to module imports
• Switched inaccessible <CanvasSpinner> to <Spinner> from @wordpress/components
• Removed any build-tools specific files and code
• Updated prettier config to point to WordPress standards
• Removed some unused files from the plugin

How has this been tested?

This has been tested locally to ensure that both the watch:dev and build:prod commands produce the required built asset files, and that these files are enqueued successfully in the editor.

Functionality has been checked to ensure that it remains the same as prior to this change.

The readme has been updated to ensure it reflects the updated build process.

[chrishbite]

Just one small change, everything else looks good 👍