RFR: 8259377: Shenandoah: Enhance weak reference processing timing tacking [v2]

[Zhengyu Gu]

> Please review this enhancement for tracking weak references processing.
> 
> Test:
> - [x] hotspot_gc_shenandoah

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

  Fix indentations

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1979/files
  - new: https://git.openjdk.java.net/jdk/pull/1979/files/a01325d9..baa53fa8

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1979&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1979&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1979.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1979/head:pull/1979

PR: https://git.openjdk.java.net/jdk/pull/1979