REST views: Improved UX of exposed sorts in collections

Problem/Motivation

When creating exposed sorts for collections, the Views UI does not provide insight into the parameter structure for the querystring. As a result, developers unfamiliar with the URL syntax will need to create a "regular" view, save it, navigate to the page, and experiment with the exposed form to see what it does. The Views UI should surface more of the key identifiers.

Proposed resolution

Much like exposed fields will show you the identifier for the field's querystring parameter in the field plugin's modal popup, the exposed search popup should provide insight into the sort_by, sort_order properties and their accepted values. This might be mitigated by a module such as Self-Documenting REST API providing this information.

Remaining tasks

Determine approach

User interface changes

Additions to the views admin UI.

API changes

None expected.

Data model changes

None expected.