RFR: Incorrect constant folding with final field and -ShenandoahOptimizeFinals

[Roland Westrelin]

http://cr.openjdk.java.net/~roland/shenandoah/ccpfinalfieldrb/webrev.00/

I ran some tests with -ShenandoahOptimizeFinals and I found we would
sometime incorrectly constant fold loads of final fields. During CCP,
when types are propagated, we must make sure we always process a Load
that is behind a read barrier when the type of the read barrier input
changes because the type of the read barrier itself doesn't change.

Roland.