Replace delegated predicate methods with boolean-returning methods

What does this MR do?

Predicate methods should return a boolean value, however when we delegate with allow_nil to properly handle non-extant relations, we end up with true, false, and nil as possible responses. While we generally are loose about nil being equivalent to false in Ruby, I feel like a predicate method is a special signal that we very much care about the boolean nature of its response.

A continuation of !54262 (merged) and !54610 (merged) Related to #322100