libstdc++: Format empty chrono-spec for the time points and hh_mm_ss directly.

libstdc++: Format empty chrono-spec for the time points and hh_mm_ss directly.

This patch change implementation of the formatters for time points and hh_mm_ss,
so they no longer delegate to operator<< for ostream in case of empty chrono-spec.
As in case of calendar types, the formatters for specific type now provide
__formatter_chrono with default _ChronoSpec that are used in case if empty
chrono-spec.

The configuration of __defSpec is straight forward, except for the sys_time,
and local_time that print time, if the duration is convertible to days,
which is equivalent to setting _M_chrono_specs "%F" instead of "%F %T".
Furthermore, certain sys_time<Dur> do not support ostream operator, and
should not be formattable with empty spec - in such case default
_M_chrono_spec, allowing the issue to still be detected in _M_parse.

Finally, _ChronoFormats are extended to cover required format strings.

libstdc++-v3/ChangeLog:

	* include/bits/chrono_io.h (_ChronoFormats::_S_ftz)
	(_ChronoFormats::_S_ft, _ChronoFormats::_S_t): Define.
	(__formatter_chrono::_M_format_to_ostream): Remove handling for
	time_points.
	(std::formatter<chrono::hh_mm_ss<_Dur>, _CharT>)
	(std::formatter<chrono::sys_time<_Dur>, _CharT>)
	(std::formatter<chrono::utc_time<_Dur>, _CharT>)
	(std::formatter<chrono::tai_time<_Dur>, _CharT>)
	(std::formatter<chrono::gps_time<_Dur>, _CharT>)
	(std::formatter<chrono::file_time<_Dur>, _CharT>)
	(std::formatter<chrono::local_time<_Dur>, _CharT>)
	(std::formatter<chrono::__detail::__local_time_fmt<_Dur>, _CharT>)
	(std::formatter<chrono::zoned_time<_Dur>, _CharT>):
	Define __defSpec, and pass it as argument to _M_prase and
	constructor of __formatter_chrono.