RFR: 8340183: Shenandoah: Incorrect match for clone barrier in is_gc_barrier_node

[Aleksey Shipilev]

The name of the call we emit is "shenandoah_clone":
https://github.com/openjdk/jdk/blob/545951889c1ea68646be600decaf2bf4c049600b/src/hotspot/share/gc/shenandoah/c2/shenandoahBarrierSetC2.cpp#L806

...yet we test for "shenandoah_clone_barrier" here:
https://github.com/openjdk/jdk/blob/545951889c1ea68646be600decaf2bf4c049600b/src/hotspot/share/gc/shenandoah/c2/shenandoahBarrierSetC2.cpp#L688

I think we are better off polling the call target instead of relying on call name. This change also eliminates `shenandoah_cas_obj` matcher, for which we do not have the emitted call ever since we started doing CAS expansions inline.

Additional testing:
 - [x] Linux x86_64 server fastdebug, `hotspot_gc_shenandoah`
 - [ ] Linux x86_64 server fastdebug, `all` with `-XX:+UseShenandoahGC`

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Commit messages:
 - Fix

Changes: https://git.openjdk.org/jdk/pull/21014/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21014&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8340183
  Stats: 20 lines in 3 files changed: 6 ins; 10 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/21014.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21014/head:pull/21014

PR: https://git.openjdk.org/jdk/pull/21014