migrate to block.json for block registration

https://github.com/AdvancedCustomFields/acf/issues/654#issue-1234061176 has several nuggets of information and things that I will need to do including:

any action items? eventually I'll need to migrate to block.json (I think?>) https://github.com/AdvancedCustomFields/acf/issues/654#issuecomment-1125329188

(the related commit is just to commit the block.json file; the block registration, etc, is still happening in php; for now)

TODO:

• only display the block CSS when block is used on that page (this happens in the main branch)
• delete the libcal-block.css file