Children items in Dropdown menus should receive keyboard focus

[HaSistrunk]

Describe the bug

Dropdown menu items do not receive keyboard focus when navigating the dropdown menus with a keyboard.

To reproduce

Steps to reproduce the behavior:
For the MyListDropdown component:

1. Go to 'My List' page on mobile
2. Tab to select 'Actions' button
3. Press 'Enter' or 'Space' to open menu
4. See that first item is not selected and down arrow keys do not select/focus on dropdown items.

Expected behavior

Focusable elements should receive keyboard focus just as shown in the React Accessible Dropdown Menu Hook demo.

Additional context

The NavDropdown component items do receive focus via the Tab key, which works ok but does not follow the expected pattern of using arrow keys.