Update Quiz creation to reference unique questions by way of the item property

[nucleogenesis]

Overview

Quiz questions use a composite ID joining the question's exercise_id (the Exercise it came from) and it's question_id, an ID for the question within that particular Exercise. This is to avoid collisions if two Exercises have the same question_id in them.

Elsewhere in the codebase, we use the same type and shape of ID -- for example, in logging.

In those cases, each question-shaped object has a property item to reference this unique ID. We should do this everywhere!

Acceptance criteria

• Update quizCreationSpecs.js definition of id and change it to item.
• Reviewing useQuizCreation selectQuestions and the components in <coach>/../plan/CreateExamPage/* - revise naming throughout to no longer reference "Question IDs" as a concept when, in fact, it is referencing the Question Item. The changes here should distinguish between a question's question_id -- in which case the naming convention referencing "Question ID" would make sense.

For example, in selectQuestions.js the 4th parameter questionIdArrays is actually referencing a question's "item", so perhaps questionItemArrays would make more sense.

Similar instances can be found throughout (ex1, ex2, ex3