[Bug]: Update Dropdown, Combobox & Multiselect focus states

[Kritvi-bhatia17]

Acceptance criteria

Background: Michael highlighted some differences in interaction and behavior across several Dropdown variants, including Combobox, Multiselect, Filterable Multiselect, Multiselect with Select All, and Fluid Dropdown with no default option. Specifically, a few of the focus states need adjustments. We discussed this further in the CAG call (Oct 21).
(Related figma kit issue)

Tasks

• Update the focus state for all dropdown variants (both default & fluid) based on following interactions:
  • Mouse & 'Enter' key
  • Down arrow key

Refer to: Figma kit