RFR: 8202110: (fs) Default file system provider should load UnixNativeDispatcher lazily

[Brian Burkhalter]

Initialize `needToResolveAgainstDefaultDirectory` instance variable lazily thereby deferring early use of `UnixNativeDispatcher` and hopefully loading `libnio`.

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Commit messages:
 - 8202110: (fs) Default file system provider should load UnixNativeDispatcher lazily

Changes: https://git.openjdk.org/jdk/pull/13132/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13132&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8202110
  Stats: 53 lines in 1 file changed: 29 ins; 24 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/13132.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13132/head:pull/13132

PR: https://git.openjdk.org/jdk/pull/13132