RFR: 8325199: (zipfs) jdk/nio/zipfs/TestPosix.java failed 6 sub-tests

[Eirik Bjørsnøs]

Please review this PR which fixes an intermittent failure on Windows for the `TestPosix` test.

The recently introduced test `setPermissionsShouldConvertToUnix` fails to close the `FileSystem` returned by `createEmptyZipFile`. The solution is to move this call within the 'try-with-resources' statement, ensuring it gets properly closed.

Besides fixing the underlying file resource management issue, this PR also re-enables this test on Windows.

Since the author failed to realize that the method `createEmptyZipFile` returns an open FileSystem, this PR also suggests that we rename this method to `createEmptyZipFileSystem` in the hope that it will reduce future confusion.

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Commit messages:
 - Note that the caller is responsible for closing the FileSystem returned by createEmptyZipFileSystem
 - Re-enable the setPermissionsShouldConvertToUnix test on Windows
 - createEmptyZipFile returns an open FileSystem, make sure we close it in a try-with-resources

Changes: https://git.openjdk.org/jdk/pull/17702/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17702&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8325199
  Stats: 13 lines in 2 files changed: 1 ins; 7 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/17702.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17702/head:pull/17702

PR: https://git.openjdk.org/jdk/pull/17702