RFR(S): 8226778 [JVMCI] Handle unpacking properly in Deoptimziation::get_cached_box()

[Igor Veresov]

This is a forward port of the change to jvmci-8. It fixes a problem with decoding of StackValue on big-endian platforms.
The fix is for JDK13, with intention do be automatically forward ported to JDK14. 

Webrev: http://cr.openjdk.java.net/~iveresov/8226778/webrev.00/ <http://cr.openjdk.java.net/~iveresov/8226778/webrev.00/>

Thanks!
igor