Fix formatDateRange's handling of all-day events.

Android's formatDateRange's interpretation of a time span running until 0 ms
into a day is different from icu4c. Traditionally we didn't count that as
being the next day, but icu4c does.

Bug: 10560853
Change-Id: I99fbbf19ad98147c9c4ff568231aec71d97a8938

Conflicts:
	luni/src/main/java/libcore/icu/DateIntervalFormat.java
	luni/src/test/java/libcore/icu/DateIntervalFormatTest.java