[Platform] Change implementation of LocaleICU class to support more UDateFormat.

[Platform] Change implementation of LocaleICU class to support more UDateFormat.
https://bugs.webkit.org/show_bug.cgi?id=89967

Reviewed by Kent Tamura.

This patch changes internal functions of LocaleICU class to process
multiple ICU date time format handles in addition to short date time
format handle.

This patch is a part of implementing input type time. I'll add time
format related ICU date time format handles.

No new tests. This patch doesn't change behavior.

* platform/text/LocaleICU.cpp:
(WebCore::LocaleICU::initializeShortDateFormat): Changed to use openDateFormat().
(WebCore::LocaleICU::openDateFormat): Added for common usage of udt_open().
(WebCore::getDateFormatPattern): Added for common usage of udt_toPattern().
(WebCore::localizeFormat): Changed to take String parameter.
(WebCore::LocaleICU::initializeLocalizedDateFormatText): Changed to use getDateFormatPattern.
(WebCore::LocaleICU::createLabelVector): Changed to take UDateFormat parameter.
(WebCore::LocaleICU::initializeCalendar): Changed for helper functions.
* platform/text/LocaleICU.h:
(LocaleICU):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@121321 268f45cc-cd09-0410-ab3c-d52691b4dbfc