[Passage] Change screenreader text for [[1]] and [2]
[Passage] Change screenreader text for [[1]] and [2]

Summary:
Changes the screenreader text for [[1]] to be "question marker one",
and for [2] to be "sentence two".

Test Plan:
Visit [this passage item](http://localhost:9000/test.html#content=%7B%22question%22%3A%7B%22content%22%3A%22%5B%5B%E2%98%83%20passage%201%5D%5D%5Cn%5Cn%5B%5B%E2%98%83%20passage-ref%201%5D%5D%22%2C%22images%22%3A%7B%7D%2C%22widgets%22%3A%7B%22passage%201%22%3A%7B%22type%22%3A%22passage%22%2C%22graded%22%3Atrue%2C%22options%22%3A%7B%22passageTitle%22%3A%22%22%2C%22passageText%22%3A%22Hi%20%5B%5B4%5D%5D%20question%20indicator.%20%5B2%5D%20aaaaaaaaaa%20%5B%5B6%5D%5D%22%2C%22footnotes%22%3A%22%22%2C%22showLineNumbers%22%3Atrue%7D%2C%22version%22%3A%7B%22major%22%3A0%2C%22minor%22%3A0%7D%7D%2C%22passage-ref%201%22%3A%7B%22type%22%3A%22passage-ref%22%2C%22graded%22%3Atrue%2C%22options%22%3A%7B%22passageNumber%22%3A1%2C%22referenceNumber%22%3A1%7D%2C%22version%22%3A%7B%22major%22%3A0%2C%22minor%22%3A0%7D%7D%7D%7D%2C%22answerArea%22%3A%7B%22type%22%3A%22multiple%22%2C%22options%22%3A%7B%22content%22%3A%22%22%2C%22images%22%3A%7B%7D%2C%22widgets%22%3A%7B%7D%7D%2C%22calculator%22%3Afalse%7D%2C%22itemDataVersion%22%3A%7B%22major%22%3A0%2C%22minor%22%3A1%7D%2C%22hints%22%3A%5B%5D%7D)
and inspect the output.

Reviewers: kitt, john

Reviewed By: john

Subscribers: #a11y

Differential Revision: https://phabricator.khanacademy.org/D17740

ariabuckles/perseus,abe4mvp/perseus,learningequality/perseus,ariabuckles/perseus,ariabuckles/perseus,daukantas/perseus,sachgits/perseus,ariabuckles/perseus,abe4mvp/perseus,learningequality/perseus,alexristich/perseus,sachgits/perseus,iamchenxin/perseus,chirilo/perseus,iamchenxin/perseus,daukantas/perseus,alexristich/perseus,chirilo/perseus