RFR: 8272905: Consolidate discovered lists processing [v3]

[Albert Mingkun Yang]

> Simple change of merging discovered list processing for four kinds of non-strong refs and some general cleanup around.
> 
> Test: tier1-3

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

  review

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/5242/files
  - new: https://git.openjdk.java.net/jdk/pull/5242/files/3650b5d6..dbbfff4d

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=5242&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=5242&range=01-02

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5242.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5242/head:pull/5242

PR: https://git.openjdk.java.net/jdk/pull/5242