RFR: 8364954: (bf) CleaningThread should be InnocuousThread [v2]

[Liam Miller-Cushon]

> This migrates a `Thread` introduced in [JDK-8344332](https://bugs.openjdk.org/browse/JDK-8344332) to use `InnocuousThread`, similar to the changes in [JDK-8345432](https://bugs.openjdk.org/browse/JDK-8345432) to migrate other uses of `Thread` in `java.nio` to `InnocuousThread`.

Liam Miller-Cushon has updated the pull request incrementally with one additional commit since the last revision:

  Remove '= null'

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/26665/files
  - new: https://git.openjdk.org/jdk/pull/26665/files/89394ce2..d306f87b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26665&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26665&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/26665.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26665/head:pull/26665

PR: https://git.openjdk.org/jdk/pull/26665