This was an oversight in e42d954743.
These fields should always follow the locale preference in the CLDR.
Overriding these fields would permit formats like "h:mm:ss" to result in
strings like "1:2:3" instead of "1:02:03".
TR-35's Matching Skeleton algorithm dictates how user requests including
fractional second digits should be handled when the CLDR format pattern
does not include that field. When the format pattern contains {second},
but does not contain {fractionalSecondDigits}, generate a second pattern
which appends "{decimal}{fractionalSecondDigits}" to the {second} field.
This is not a calendar supported by ECMA-402, so let's not waste space
with its data.
Further, don't generate "gregorian" as a valid Unicode locale extension
keyword. It's an invalid type identifier, thus cannot be used in locales
such as "en-u-ca-gregorian".
This adds plumbing for the Intl.DateTimeFormat object, constructor, and
prototype.
Note that unlike other Intl objects, the Intl.DateTimeFormat object has
a LibUnicode structure as a base. This is to prevent wild amounts of
code duplication between LibUnicode, Intl.DateTimeFormat, and other
not-yet-defined Intl structures, because there's 12 fields shared
between them.
