Replace ICU.getAvailableCollatorLocales() with ICU4J Collator.getAvailableLocales

libcore's Collator can delegate the calls to ICU4J because
libcore's Collator and ICU4J's Collator do not have circular runtime dependency.

Bug: 138994281
Test: atest CtsLibcoreTestCases:libcore.java.util.LocaleTest
Change-Id: I5e14eeb1d25ecba76dd8807c4b5600a8d8cad5cd
3 files changed