RFR: JDK-8219245: Shenandoah: Resolve oops in SATB filter

[Roman Kennke]

When updating reference is piggy-backed on marking phase, we need to
resolve oops that we get in SATB buffers before checking if they are
marked, because from-space oops never get marked. This generates
unnecessary traffic in SATB.

Fix is to add template to requires_marking() that optionally resolves
the object, and use that when we may see forwarded objects.

Bug:
https://bugs.openjdk.java.net/browse/JDK-8219245
Webrev:
http://cr.openjdk.java.net/~rkennke/JDK-8219245/webrev.00/

Testing: hotspot_gc_shenandoah looks good

Ok?

Roman

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