Quick: Eliminate check-cast guaranteed by instance-of.

Eliminate check-cast if the result of an instance-of with
the very same type on the same value is used to branch to
the check-cast's block or a dominator of it.

Note that there already exists a verifier-based elimination
of check-cast but it excludes check-cast on interfaces. This
new optimization works for interface types and, since it's
GVN-based, it can better recognize when the same reference
is used for instance-of and check-cast.

Change-Id: Ib315199805099d1cb0534bb4a90dc51baa409685