Some locales do not define morning, night, etc. day period ranges.
TR-35 states they should fall back to the fixed day periods AM and PM.
Add a test case for the "as" locale, which is one such locale, to ensure
its AM/PM symbols are used.
For the test cases changed here, we now recognize "morning2" and
"afternoon2" from the CLDR, so the expected results now match the specs
and other engines.
There are a few FIXMEs that will need to be addressed, but this
implements most of the prototype method. The FIXMEs are mostly related
to range formatting, which has been entirely ignored so far. But other
than that, the following will need to be addressed:
* Determining flexible day periods must be made locale-aware.
* DST will need to be determined and acted upon.
* Time zones other than UTC and calendars other than Gregorian are
ignored.
* Some of our results differ from other engines as they have some
format patterns we do not. For example, they seem to have a lonely
{dayPeriod} pattern, whereas our closest pattern is
"{hour} {dayPeriod}".
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.
