Dropdown: typeahead not available

[theetrain]

Based on discussion: #1974

Problem

When focusing on a Dropdown, typing a value should open the dropdown and focus on the first matching item.

React demo: https://carbondesignsystem.com/components/dropdown/code/
Svelte demo: https://svelte.carbondesignsystem.com/framed/Dropdown/DropdownSlot?theme=white

[snaxks]

The is already a ComboBox component that lets you type and filter items. I don't think this is needed functionality for the Dropdown component