Move attempt's questions randomization into a proper static method

[eri-trabiccolo]

Description

Needed to fix the issues with questions bank randomization.

How has this been tested?

manually

Screenshots

Types of changes

Bug fix (non-breaking change which fixes an issue)/Enhancement.

Checklist:

• [x] This PR requires and contains at least one changelog file. <!-- To create a changelog yml file: npm run dev changelog add -- -i and follow the prompt. See also: https://github.com/gocodebox/lifterlms/blob/trunk/packages/dev/README.md#changelog-add -->
• [x] My code has been tested.
• [x] My code passes all existing automated tests.
• [x] My code follows the LifterLMS Coding & Documentation Standards.