Support querying through one-to-many relations

[Artem Zakharchenko]

const db = factory({ user: { post: manyOf('post') } })

// Returns the list of users who have at least one "post"
// with a title matching one of the provided titles.
db.user.findMany({
  which: {
    post: {
      title: {
        in: ['First post', 'Second post']
      }
    }
  }
})

Expected behavior

// Given these users
db.user.create({
  id: 1,
  posts: [db.post.create({ title: 'First post' })]
})

db.user.create({
  id: 2,
  posts: [db.post.create({ title: 'Second post' }), db.post.create({ title: 'Third post' })]
})

db.user.create({
  id: 3,
  posts: [db.post.create({ title: 'Fourth post' })]
})

// Should return the following users:
[1, 2]

Current behavior

Failed to find a comparator for the value "[...]"