Show query help

Problem/Motivation

Every schema can define its own query syntax, and the user may have no idea how to fill out the Query field on the property edit form. #2474111: Provide autocomplete for schema property query will help but a description of the syntax, preferrably with example(s) and link to formal definition, would help to get started.

Proposed resolution

Add a method to the query evaluator interface, that can return a renderable array for the help. Display it near the Query input field in the property form.

Remaining tasks

User interface changes

API changes