[sumac] feat: handle unsaved changes in text & problem editors (#1444)

[navinkarkera]

The text & problem xblock editors will display a confirmation box before cancelling only if user has changed something else it will directly go back.

(cherry picked from commit df8a65d)

Backport of #1444

[openedx-webhooks]

Thanks for the pull request, @navinkarkera!

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