search: design proposals for AND / OR / NOT expressions

Created by: rvantonder

A subtask of #7823 (closed) is to define the constraints and behaviors for implementing AND / OR / NOT expressions. The progress on this task so far is:

• A design proposal for the Query Predicate Language, RFC 94
• A proposal to change literal search so that we can support the query predicate language universally, RFC 108. This RFC is abandoned and we will not implement AND / OR expressions for literal search initially due to conflicting design decisions in the input representation.