RFR: 8258490: Shenandoah: Full GC does not need to remark threads and drain SATB buffers [v2]

[Zhengyu Gu]

> Full GC marks heap at a pause with SATB deactivated, therefore, we don't need to remark threads and drain SATB buffers during final mark phase.
> 
> - [x] hotspot_gc_shenandoah

Zhengyu Gu has updated the pull request incrementally with one additional commit since the last revision:

  Minor update

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1805/files
  - new: https://git.openjdk.java.net/jdk/pull/1805/files/7178b3b0..602347da

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1805&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1805&range=00-01

  Stats: 3 lines in 1 file changed: 1 ins; 2 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1805.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1805/head:pull/1805

PR: https://git.openjdk.java.net/jdk/pull/1805