Test the dropdown (select) function for accessibility

[cjrace]

We had a recent accessibility audit at DfE that highlighted a few issues with standard shiny dropdown selectors. We should review whether the select function in this package would solve those issues by testing the test / template app ourselves. I believe it should, though not all GDS components are fully accessible, so this is worth checking specifically as a part of the upgrade to v5+ of the frontend system.

Examples of issues with other dropdowns we should test:

• Having a visual label marked up
• Having a non-visual label marked appropriately
• Appropriate contrast on focus

I have specific examples I can share on this to have a look at from our accessibility audit.