Fix libcore.libcore.icu.DateIntervalFormatTest#testEndAtMidnight

The test was asserting that the calendar year is not part of the
formatted result, even though it is (for years in the past).

This CL updates the test for the fact that 2018 is now a previous
year. The CL adds a test for the case where start and end are in
different years.

Test: atest CtsLibcoreTestCases:libcore.libcore.icu.DateIntervalFormatTest
Bug: 122240208

Change-Id: I6ebe990349b8a131e2f5611022eb575002f49730