RFR: 8269596: Snapshot soft ref policy before marking/copying [v3]

[Albert Mingkun Yang]

> Set up soft ref policy before marking/copying for Serial, Parallel and G1. With this change, all collectors do soft-ref policy setup in the beginning of a GC cycle.

Albert Mingkun Yang has updated the pull request incrementally with one additional commit since the last revision:

  restore

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/4624/files
  - new: https://git.openjdk.java.net/jdk/pull/4624/files/ca0e71eb..6ba25591

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4624&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4624&range=01-02

  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4624.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4624/head:pull/4624

PR: https://git.openjdk.java.net/jdk/pull/4624