Improve fidelity of approximation to CLDR zone representations

I neglected to update the CLDR dateconverter code when I expanded the
range of forms we support for display of a timezone. Even that
expanded range doesn't cover all the cases CLDR does, but we can at
least approximate each of CLDR's options by the closest we do support.
Make matching changes to how the Darwin backend for the system locale
maps its ICU-derived formats to ours.

This in practice changes all locales previously using t (abbreviation)
as zone format to use tttt (IANA ID) instead. Test data updated to
match.

[ChangeLog][QtCore][QLocale] Date-time formats now more faithfully
follow the CLDR data in handling timezones. In most cases this means
the IANA ID is used in place of the abbreviation.

Change-Id: I0276843085839ba9a7855a78922cffe285174643
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>