RFR: 8260004: Shenandoah: Rename ShenandoahMarkCompact to ShenandoahFullGC

[Zhengyu Gu]

Please review this patch that renames ShenandoahMarkCompact to ShenandoahFullGC, to be consistent with other GCs.

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Commit messages:
 - JDK-8260004-rename-fullgc

Changes: https://git.openjdk.java.net/jdk/pull/2266/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2266&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8260004
  Stats: 38 lines in 9 files changed: 4 ins; 6 del; 28 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2266.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2266/head:pull/2266

PR: https://git.openjdk.java.net/jdk/pull/2266