Fix DatePicker's spinner order in various locales.

DatePicker always effectively uses yyyy MMM dd, so we need to ask
icu4c what order those should appear in for the user's locale. The
existing DateFormat code was an approximation that worked for en_US
but not for all languages (fa being one example).

Bug: 7207103
Change-Id: I7b12568dbc02522ebad6e1db5f8426109cd6f7ce