Improve accessibility of Admin Course button

[damianhxy]

Description

This PR implements the relevant aria code from the assessment view page to the manage course page. It also replaces the obsolete onkeypress event with onkeydown.

Motivation and Context

Similar to #1215, adding the aria-expanded attribute improves accessibility.

How Has This Been Tested?

Checked that the dropdowns have the correct initial aria-expanded attribute (true for admin course and false for admin autolab). Also checked that clicking on a dropdown, or tabbing to a dropdown and pressing the enter key, toggles the aria-expanded attribute correctly.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have run rubocop for style check. If you haven't, run overcommit --install && overcommit --sign to use pre-commit hook for linting
• My change requires a change to the documentation, which is located at Autolab Docs
• I have updated the documentation accordingly, included in this PR

Other issues / help required

If unsure, feel free to submit first and we'll help you along.

[najclark]

I made some suggested changes regarding the drag/drop handin functionality.

[najclark]

LGTM

[xinyis991105]

LGTM!