[v3] Extract Concepts from v2 exercise: protein-translation

Extract the list of concepts required to solve the v2 C++ exercise: `protein-translation`. For each concept, describe why it is required to solve the exercise. Keep in mind that an exercise can have multiple approaches (you can find community solutions here: `https://exercism.io/tracks/cpp/exercises/protein-translation/solutions`). The goal of this task is to help determine the total list of concepts that make up `protein-translation`.

The list of concepts should be stored in the following document: `languages/cpp/reference/exercise-concepts/protein-translation.md`. [Use this link to create a PR to add this document][pr-link].

[pr-link]: ../new/master?filename=languages/cpp/reference/exercise-concepts/protein-translation.md

Review the v2 C++ protein-translation exercise and the linked community solutions, then create languages/cpp/reference/exercise-concepts/protein-translation.md. Record every concept needed by the exercise and explain why it is required, including concepts used by different solution approaches. Done means the document covers the full concept list and its rationale.

Written by the indexing model from the issue text.