In some time zones, date form field sets itself to the wrong date

Problem/Motivation

When the site's/user's time zone is UTC, the widget works as expected. However, with time zones behind UTC (e.g. New York or Honolulu), it does not. When the user selects a date, the date field sets itself to the day before the selected one.

Steps to reproduce

• Basic setup:
  • Set up a fresh Drupal 9 site with facets_date_range enabled.
  • Set up a content type with a date field (date only, no time).
  • Create a few nodes with different dates.
  • Set up a database search server, search index, and view of the search index with a page display.
  • Set up a facet for the date field, with the Date Range Picker widget and facet setting selected.
  • Add the facet block to the search page.
• Key steps to reproduce the bug:
  • In Configuration > Regional Settings, change the default time zone to Honolulu. Uncheck "Users may set their own time zone".
  • On the search page, use the facet's calendar widget to select a date, e.g. 2022.03.30.

The URL shows the timestamp for the expected date, e.g. 1648598400 = 2022.03.30 00:00:00 +0000. But the date field shows the wrong date, e.g. 2022.03.29.

Proposed resolution

When the code converts between dates and timestamps, consistently use UTC. (I'll submit a merge request shortly.)