Consolidate code to add custom fields to form

[eileenmcnaughton]

Overview

Proposal for consolidating code for custom data on forms (initial step)

Before

no change

After

no change

Technical Details

@mattwire looking at #11805 I'm wondering if we should do some steps like this first?

Comments

I retained

• $this->set('type', $type);
• $this->set('subType', $subType);
• $this->set('entityId', $entityId);

But have some doubts about those lines

[mattwire]

Ref #11794

[mattwire]

@eileenmcnaughton This looks good... I've just proposed #11910 which takes this a little bit further.

[mattwire]

Not sure if $this->set... lines are required either.

[eileenmcnaughton]

@mattwire I'm going to close both of these as they are still both WIP. I will try to put some more time in soon & will re-open one or both when they seem merge ready