Add change comments in DecimalFormatsSymbols.

Add Android-changed/-removed/-added comments where appropriate in
java.text.DecimalFormatSymbols.

This also applies a small upstream change when checking for empty
country value. This is change does not change behaviour, as
Locale.getCountry() is guaranteed to never return null.

Bug: 65669355
Test: CtsLibcoreTestCases
Change-Id: I55fab57d63c53b6885675a75157e86d9c796f521
1 file changed