RFR: 8344461: Additional cleanup in NewThreadAction [v2]

[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.

Stuart Marks has updated the pull request incrementally with one additional commit since the last revision:

  Make thread group fields final.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/22557/files
  - new: https://git.openjdk.org/jdk/pull/22557/files/a9999f19..8008ae74

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=22557&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=22557&range=00-01

  Stats: 3 lines in 1 file changed: 1 ins; 0 del; 2 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