Implement getDateFormatOrder.

I do wonder if we shouldn't generalize this, rather than hard-code yMd,
but YAGNI.

Bug: 7207103
Change-Id: Ib59191eee97c08913f9a0a4ea52fb6eb8c677918
Fixes for icu4c 51.

Change getYesterdayTodayAndTomorrow to cope with the new data layout.

Extend getDateFormatOrder to cope with 'G' in fa's preferred yyyyMMdd
pattern.

Fix a few tests to correspond to data changes.

Change-Id: I2478ae960ff6ec0b9a95290132c0ae0d5d8eff5a

Conflicts:
	luni/src/test/java/tests/api/java/util/LocaleTest.java
Remove the isLocaleAvailable hacks.

Change-Id: I17596301630f6c8d98c4415fe358f4fffb47b2d4