[FEATURE] Enable sheet compacting in individual Flux forms

WARNING: DO NOT USE DYNAMIC VARIABLES!
WARNING: IS DESTRUCTIVE WHEN CHANGED IN AN EXISTING ELEMENT!

Be very careful about this new toggle. Only use it in absolutely fresh content element templates - once data has been saved in either state, toggling the state destroys the database content; it can even potentially cause "invalid argument type for foreach" errors when using section objects in Flux forms.

In short: there are some pitfalls but using it on all new content templates is completely safe.