RFR: 8261036: Reduce classes loaded by CleanerFactory initialization

[Claes Redestad]

This patch refactors CleanerFactory and InnocuousThread so that we need to load fewer PrivilegedActions. This slightly reduce the number of classes we always load on bootstrap, slightly reducing static and dynamic footprint (default CDS archive -4Kb).

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Commit messages:
 - Reduce classes loaded by CleanerFactory initialization

Changes: https://git.openjdk.java.net/jdk/pull/2380/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2380&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8261036
  Stats: 49 lines in 2 files changed: 26 ins; 9 del; 14 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2380.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2380/head:pull/2380

PR: https://git.openjdk.java.net/jdk/pull/2380