RFR: 8367347: Serial: Refactor CLDScanClosure

[Francesco Andreuzzi]

Refactor `CLDScanClosure` so that all CLD logic is encapsulated in the CLD closure, without polluting the oop closure.

Test: tier1-2, running tier3

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Commit messages:
 - double space
 - refactor

Changes: https://git.openjdk.org/jdk/pull/27199/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27199&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8367347
  Stats: 21 lines in 1 file changed: 3 ins; 4 del; 14 mod
  Patch: https://git.openjdk.org/jdk/pull/27199.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27199/head:pull/27199

PR: https://git.openjdk.org/jdk/pull/27199