Conditional field display based on tags

[quincylvania]

Sometimes it only makes sense to display a field if certain tags are present on the feature. For example, the Payment Types field would be useful on presets such as Parking Lot, Telephone, or Toilets, but only when fee=yes. Another use would be in #5580, where the field for diet:vegetarian would be redundant if diet:vegan=yes.

I propose finding a generalized solution where conditions can be defined in JSON and not in code.

Related: #4871

[bhousel]

This sounds really hard..

[quincylvania]

@bhousel Perhaps!