Add export tab to Edit Field and Edit Template

[Toutouwai]

Short description of the enhancement

The FormBuilder module has this useful field in the "Import/Export" tab:

This request is for a similar tab/field in Edit Field and Edit Template.

The field would show the same JSON export data as you would get from...

1. Navigating to Setup > Fields/Templates
2. Clicking the Export button
3. Selecting the field/template
4. Then clicking Export.

It would just be quicker and more intuitive. Most of the time when I want to export a field or template I want to review its settings first, so I'm already in Edit Field/Template and it's a bit of a pain to have to go back to the listing page and then go through all the steps.

And if there was a JSON Import field on the same tab I wouldn't complain either. 😃

P.S. I like the FormBuilder option to download a JSON file too: #461

[jlahijani]

Related: #368