Fix harmony java.text test failures.

There were plenty of bad tests here, but there were some real bugs too.

* DecimalFormat was only handling RoundingMode.UNNECESSARY for double
formatting.

* DecimalFormat was not ensuring that it's superclass' fields were
being correctly updated.

* NumberFormat was throwing NPE for a null object because of an
improved detail message, despite being specified to throw IAE.

* We weren't mapping NumberFormat.Field instances to the corresponding icu4c
UNUM_x_FIELD constant, so we weren't actually setting FieldPosition
objects correctly.

* SimpleDateFormat was not formatting milliseconds correctly with 'S'.

* NativeDecimalFormat wasn't handling JNI NewString OOME correctly.

Bug: 2528220
Bug: 3056865
Bug: 3057080
Bug: 3057090
Change-Id: Iac11f902f2e9649e596e7e7b7bc501b13e956fca

Conflicts:
	expectations/brokentests.txt