RFR: 8337658: ZGC: Move soft reference handling out of the driver loop function [v2]

[Stefan Karlsson]

> The ZDriver code is written to be neat and have a clear outline. The soft reference handling distracts when reading this code. I propose that we hide it a bit.
> 
> I've also clarified in comments and names that the code is dealing with clearing of *all* references.

Stefan Karlsson has updated the pull request incrementally with one additional commit since the last revision:

  Fix inconsistent naming

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/20418/files
  - new: https://git.openjdk.org/jdk/pull/20418/files/5a69a95e..c84a143e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20418&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20418&range=00-01

  Stats: 5 lines in 2 files changed: 0 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/20418.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20418/head:pull/20418

PR: https://git.openjdk.org/jdk/pull/20418