While introducing Calendar2 and the XCalendar3 interface anyway, as well the
"one letter" narrow month names sometimes needed in calendaring can be added.
These are not always the first capitalized letters of the months in all
locales, and might even not necessarily be just one character.

Introduces a new struct css::i18n::Calendar2 that is not derived from
css::i18n::Calendar because it uses a new struct css::i18n::CalendarItem2 to
hold the NarrowName elements.

In locale data the elements DaysOfMonth, MonthsOfYear and GenitiveMonths now
have an optional element DefaultNarrowName. If not specified, the first
character of DefaultFullName is taken.

LocaleDataWrapper and CalendarWrapper use and return the new Calendar2 and
sequences of CalendarItem2 structs. Application code adapted.

The number formatter now displays narrow month names (genitive if applicable)
for the MMMMM code, previously it displayed the first 16 bit code point of the
full name (not even utf-16 aware).

Narrow day names currently are not used, except in svtools' Calendar control.