refactor: replace fx-layout with tailwind equivalent - unit-dropdown

[satikaj]

Description

Replaced the fx-layout usage in the unit-dropdown component with the Tailwind equivalent due to the deprecation of the fx-layout library.

Type of change

• 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 not work as expected)
• This change requires a documentation update

How Has This Been Tested?

1. Run the doubtfire-deploy dev container to start the front-end and back-end.
2. Login with the test student account (student_1).
3. Click on the Select Unit dropdown to compare looks.

Before

After

Testing Checklist:

• Tested in latest Chrome
• Tested in latest Safari
• Tested in latest Firefox

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings

[satikaj]

@williamalowe will be reviewing this.

[williamalowe]

Reviewed on 25/11/2023
-All fxLayout properties have been replaced with appropriate Tailwindcss equivalents.
-Changes does not throw any terminal errors.
-Before and After images are reproducible and appear identical.
-Inspection with browser dev tools shows exact same spacings.
Ready for second review

[maddernd]

I have also tested this,

Code looks good, runs correctly and looks correctly on my local build.

[maddernd]

This one is good to go for upstream creation to doubtfire-lms

[satikaj]

Upstream pull request has already been created doubtfire-lms#771