RFR: 8316137: GenShen: missing ShenandoahCardBarrier filter

[Y. Srinivas Ramakrishna]

A few instances of (inline) calls to the card-barrier code from the VM missed the idiomatic changes in the parent ticket https://bugs.openjdk.org/browse/JDK-8315247. This PR takes care of the cases that I had previously missed where we were doing a generational mode check on the heap.

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Commit messages:
 - More
 - Another instance.
 - Fix assertion message.
 - ShenandoahCardBarrier

Changes: https://git.openjdk.org/shenandoah/pull/322/files
 Webrev: https://webrevs.openjdk.org/?repo=shenandoah&pr=322&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8316137
  Stats: 27 lines in 2 files changed: 12 ins; 3 del; 12 mod
  Patch: https://git.openjdk.org/shenandoah/pull/322.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah.git pull/322/head:pull/322

PR: https://git.openjdk.org/shenandoah/pull/322