Remove @hide from Java 6 API.

I've left the two new spi packages @hidden, because I think we shouldn't
support them without convincing demand from developers (and I don't
believe there could be such a thing --- they just don't make sense, and
if we add anything, it should be the ability to provide extra ICU data).

Also fix a handful of javadoc syntax errors in Arrays.java and TreeMap.java.

Bug: 2497395
Change-Id: I4176b72daff0face4ed6c7ee1d1f4267d52006b4
40 files changed