Unmask Enumerable#find on one to many associations

I found myself on the console today trying to debug an issue by looking at mongoid documents:

$ items.find { |item| item["uuid"] == "1234" }

=> nil

$ items.select { |item| item["uuid"] == "1234" }.any?

=> true

In this case, `items` is an instance of `Mongoid::Criteria`, and the `find` being executed was `Mongoid::Criteria::Findable#find`, rather than the `Enumerable#find` which I expected. (Items is defined in another method, in another file, elsewhere, so I had forgotten it was a `Mongoid::Criteria` rather than simply an Enumerable)

I propose that we add a `Mongoid::Criteria#find` which routes to the appropriate find method based on the passed arguments