Add a regression test for ULocale's root/und/empty langtags handling

In ICU 64.2 locale ID handling for "", "und" and "root" has been justified.

 * ULocale.getLanguage() will return an empty string for each of these
 * ULocale("und_IN").getName() will be "_IN" for consistency

Test: atest CtsIcuTestCases:android.icu.extratest.util.ULocaleTest
Change-Id: I43a352f014d05a001929f1efd3d114635775a2b1
1 file changed