Improve and align date & time screens with the rest of settings

This is part 1 of the changes to update the date&time region and
time zone picker screens in settings. The detail of the changes made are
below:

* Updates the region picker, region zone picker and fixed offset picker
  to align with thr rest of settings.
* Adds a radio button on time zone items to show the currently selected
  time zone item.
* Ensure the item view subviews are aligned correctly based on when
  part of the subviews are hidden.
   - When the summary text and current time text is not showing, ensure
   the title text is centered.
   - When the summary text is not showing, ensure the title and the
     current time are centered.
* Removes unused icon text view, it has been replaced with  a radio
  button to show the current selection.

See details of the UI changes and screenshot at  go/date-time-ui-updates.

Flag: EXEMPT this feature is flagged with the settings wide flag
Test: manual - view ui updates in go/date-time-ui-updates
Bug: 349671765
Change-Id: Idcc7132ec28f12dfc812dc2a846feb43098dc06d