Add range date picker component variant

Problem

The date picker component for selecting a single date from the calendar dialog is being added in !616 (merged).

Proposal

Let's add a range date picker component variant for selecting a range of dates, accompanied by a calendar widget. See design proposal in !616 (comment 198197820).

We'll need to make the search box smaller to fit this in but it's doable, here's how I think we should approach it:

The horizontal spacing between the search box and the date input field should be 16px, and between the date input fields 16 px as well. Does this mockup provide enough information for this first iteration?