Make styling blocks easier

Problem/Motivation

The ability exists to add block properties that affect the display. For example you can add a select list that lets you choose different templates or adds a class to the markup. Let's standardize on a way to do this instead of keeping that a secret. We will then add examples in the +Suite Extras module.

Proposed resolution

Simply form altering the layout_builder_update_block and layout_builder_add_block forms, adding your form items to the settings group, and then saving them when submitted is enough to get it working, but our LB data modeling makes this a ton easier. Let's expose that via an BlockPropertiesEvent.