RFR: 8325399: Add tests for virtual threads doing Selector operations

[Alan Bateman]

This PR adds a new test to exercise virtual threads doing Selector operations. The test has been in the loom repo for some time as there are changes in that repo to integrate some of the Selector implementations with the poller mechanism. The test is useful to have in the main line.

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Commit messages:
 - Initial commit

Changes: https://git.openjdk.org/jdk/pull/17746/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17746&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8325399
  Stats: 349 lines in 1 file changed: 349 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/17746.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17746/head:pull/17746

PR: https://git.openjdk.org/jdk/pull/17746