RFR: 8256401: ZGC: Improve ZList verification [v2]

[Per Liden]

> The ZList verification is currently fairly weak. I propose that we make the verification stronger to easier detect corrupt lists and misuse of list nodes. This patch also removes the unused `ZList::transfer()` function.

Per Liden has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains one new commit since the last revision:

  8256401: ZGC: Improve ZList verification

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1230/files
  - new: https://git.openjdk.java.net/jdk/pull/1230/files/c729495a..20a9314b

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1230&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1230&range=00-01

  Stats: 7 lines in 1 file changed: 7 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1230.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1230/head:pull/1230

PR: https://git.openjdk.java.net/jdk/pull/1230