ENH Refactor Element to use mutation hook

[emteknetnz]

Issue #1164

Notes:

• I haven't implemented the AC "(refactor) Triggering actions on state change" - I've made a comment about it here - I don't intend to implement it though if someone is able to demonstrate a non-convoluted way to implement an alternative I'm happy to refactor
• I haven't implemented the AC "Passing down callbacks in context (note that context is required to pass props to the buttons because they're added via js injector in registerTransforms.js)" - I've made a comment about it here. I do not intend to implement this AC
• I've removed some jest tests on SaveAction-test.js and PublishAction-test.js as there is simply now less logic and props passed via context in SaveAction and PublishAction. I choose not to add in equivalent tests in Element-test.js adding in "child Actions" would require doing stuff with injector to replicate what registerTransforms.js does now, and also because these functionality is already covered by behat tests in edit-block-element.feature (save button) and publish-block-element.feature (publish button)

Update:
Don't merge this, just keep this here for reference

Got extremely stuck where somehow a second Element was being created though not actually used. Looks like it was being created as part of handleFormSchemaSubmitResponse() where state hooks were being set, though possibly something wasn't wrapped in useEffect() things got out of sync. This was detected because there was failing behat test where the page was submitted with invalid data, then immediately inline save the element, which should also fail and pop open the inline form. However the inline form wasn't popping open because the duplicated element was receiving the new props

[emteknetnz]

I tried add this to the "graphql2" PR however it caused the issue where submitting a page with an invalid elemental field and then inline saving did not pop open the preview

Don't try and make this code work, it's not necessary