RFR: 8340181: Shenandoah: Cleanup ShenandoahRuntime stubs

[Aleksey Shipilev]

Noticed this while working on Leyden, which has to enumerate Shenandoah stubs for code archival to work.

`ShenandoahRuntime::shenandoah_clone_barrier` is excessive name. `ShenandoahRuntime::arraycopy_barrier_oop_entry` and friends is not covered by `JRT_LEAF`. This change hopefully homogenizes the namings for the stubs.

Additional testing:
 - [x] Linux x86_64 server fastdebug, `hotspot_gc_shenandoah` 
 - [x] Linux AArch64 server fastdebug, `hotspot_gc_shenandoah`

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Commit messages:
 - More build fixes
 - Fix

Changes: https://git.openjdk.org/jdk/pull/21152/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21152&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8340181
  Stats: 71 lines in 9 files changed: 7 ins; 11 del; 53 mod
  Patch: https://git.openjdk.org/jdk/pull/21152.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21152/head:pull/21152

PR: https://git.openjdk.org/jdk/pull/21152