Upgrade to CLDR 23 + day period variants

CLDR 23 is out!  There are a few changes that affect ruby-cldr (and maybe a few more that I haven't found yet):

1.  Calendar fields have moved from `dates/calendars/calendar/fields` to `dates/fields`.  In other words, they're no longer a child of each calendar (i.e. there's no difference between Julian and Gregorian fields).
2.  The `layout/orientation/characters` value to determine RTL vs LTR has changed to `layout/orientation/characterOrder`
3.  CLDR no longer specifies default date/time formats.  There used to be a field for each type of date format (eg. datetime, date, time) that would specify the default width (eg. "short", "medium", "full", etc).  Those have been removed.

In addition to CLDR 23 upgrade fixes, this PR also addresses an issue that was causing calendar period variants to be exported in place of the standard periods.  For example, in English there are two possible ways to express post meridiem: "PM" the standard, and "p.m." the variant.  ruby-cldr silently overwrites "PM" with "p.m." because it happens to come later in the XML source and has the same `type` attribute.