RFR: 8344185: Remove calls to SecurityManager in sun.net.ftp

[Eirik Bjørsnøs]

Please review this PR which removes uses of `AccessController::doPrivileged` in `sun/net/ftp`.

Changes are mostly straightforward, one exception is the removal of the somewhat exotic unwrapping of temporary arrays in the static initializer of `impl/FtpClient`.

Testing: `test/jdk/sun/net/ftp` run green. GHA results pending.

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Commit messages:
 - Remove uses of AccessController::doPrivileged in FTP client

Changes: https://git.openjdk.org/jdk/pull/22105/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22105&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8344185
  Stats: 76 lines in 3 files changed: 1 ins; 54 del; 21 mod
  Patch: https://git.openjdk.org/jdk/pull/22105.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22105/head:pull/22105

PR: https://git.openjdk.org/jdk/pull/22105