[jdk17u] RFR: 8233020: (fs) UnixFileSystemProvider should use StaticProperty.userDir().

[Alex Kasko]

Clean backport of a minor fix to UnixFileSystemProvider.

Additional testing:

 - [x] ran jtreg:java/nio/file/

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

Commit messages:
 - Backport fd4de1ed404640ee0e744f022bbfa89db200ef05

Changes: https://git.openjdk.java.net/jdk17u/pull/263/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk17u&pr=263&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8233020
  Stats: 4 lines in 1 file changed: 1 ins; 2 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk17u/pull/263.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk17u pull/263/head:pull/263

PR: https://git.openjdk.java.net/jdk17u/pull/263