Throw ClassCastExceptions with good detail messages from the library.

Fix Class' methods to produce the same detail messages as the VM, remove
cruft from Arrays (so we throw the exceptions direct from the VM, like the RI
does), and fix a handful of classes that need to simulate casting because
of erasure.

Bug: 3210374
Change-Id: Ie8d1b48e069174bac60899a0530dbc8cf55fd023