Add support for Address field

Problem/Motivation

Partially filled compound fields are not validated by Require on Publish (ROP).

When partially filled, the subfields are not considered during ROP validation unless they pass their individual require validation.

Keep in mind that these contrib-module compound fields have their own required/optional setting for the subfields. Those can be set as either optional or required.

Example with Address

Address field takes it a step further by issuing the required="required" attribute, which kicks in the client-side form validation.

Steps to reproduce

1. Install Address.
2. On the Basic Page content type, create a field of type Address.
3. Leave the default require settings (Overrides for Address).
4. Ensure Require on Publish is selected on each field.
5. Create a Basic Page node; fill out only one of the required subfields, leaving the others empty.
6. Attempt to submit Draft. Fails require validation.
7. Attempt to submit Published. Fails require validation.

Proposed resolution

When a field is marked Required on Publish, we must Ensure that the required="required" attribute is removed from subfields, and either...

1. Provide module-specific field settings to mark subfields as required on publish.
2. Consider any required subfields to be required on publish.

The latter is the simpler of the two, but still may require module-specific handling because modules have different methods of creating and marking subfields as required.

Remaining tasks

Add support for compound fields.

User interface changes

Add indicators (blue carat) to subfields.