Set entity fields to hidden/view/edit/required based upon workflow state

Since workflow version 7.x-2.x, the workflow field is a 'true' field. Some modules exist to alter the appearance of a field, depending on the value of another field.

In D8 and further, this can be done using Conditional Fields module, since the Workflow State value is just another ordinary field, with a more complex widget.

This issue tries to explore the different approaches, and tries to create a battle plan.
(Note: This issue is NOT about 'alter the access of an entity, depending on the value of a (workflow) field'. That is already handled by the submodule workflow_access.)

In the past, some add-on modules have been created. The maintainers of these modules (and others) are invited to think about the future of 'Workflow Conditional Field Access':

1. Workflow Content Permissions sets field-level permissions for Content fields of node participating in a Workflow (44 sites) "On permissions page: role R can view/edit field for content type X in state Z"
2. Workflow Fields Adds per-field settings to each workflow state. (500 sites, up to 7.x-2.x) In workflow Settings page
3. Workflow Private Comments Allows to hide workflow comments based on the state of a node and role of ther user. It's basically so admins can comment about that's going on in a workflow state change without lesser roles being able to see what they said. (23 sites, up to 6.x)
4. Workflow required allows required fields to be left empty when the node is in selected workflow states. (0 sites, up to 7.x)
5. Workflow Required Fields sets requirements on fields depending on the workflow state of the node (65 sites, up to 7-1.2) In workflow Settings page
6. Workflow Field groups allows you to control which field groups may be accessed depending on the current workflow state. Control can be specified by role. Currently this only applies to form displays and not view displays. Different settings can also be set per form display mode. (1 site, D8 only)


There are also generic modules. Perhaps one of these generic modules are sufficient, since D8-Workflow is now a 'proper' field:

7. Field Permissions sett field-level permissions to create, update or view fields. (66k sites) "On field settings page: role R can create/edit/view own/any field Y on content type X"
8. Conditional Fields sets the visibility of a field, depending on the value of another field (50k sites, poorly maintained)
9. Field Conditional States is a light-weight competitor for Conditional Fields. (2k sites)