RFR: 8344461: Additional cleanup in NewThreadAction

[Stuart Marks]

Convert the RMI NewThreadAction class into a couple static methods on RuntimeUtil. Also remove a couple unnecessary qualified exports from java.base to java.rmi.

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Commit messages:
 - 8344461: clean up NewThreadAction

Changes: https://git.openjdk.org/jdk/pull/22557/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22557&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8344461
  Stats: 239 lines in 9 files changed: 88 ins; 133 del; 18 mod
  Patch: https://git.openjdk.org/jdk/pull/22557.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22557/head:pull/22557

PR: https://git.openjdk.org/jdk/pull/22557