[jdk21u-dev] RFR: 8073061: (fs) Files.copy(foo, bar, REPLACE_EXISTING) deletes bar even if foo is not readable

[Todd V. Jonker]

This is a clean backport of https://github.com/openjdk/jdk/commit/36ac83904c9e81a01822b0e36ef677cae2808709 originally authored by @bplb and reviewed by @AlanBateman  

It also includes this follow-up fix:
  * [JDK-8317128](https://bugs.openjdk.org/browse/JDK-8317128): **java/nio/file/Files/CopyAndMove.java failed with AccessDeniedException** 
      * https://github.com/openjdk/jdk/pull/15991

Additional testing:
- [x] New regression test fails without the fix, passes with it
- [x] linux-x86_64-server-release: `JTREG_KEYWORDS="!headful & !external-dep & !printer" make test TEST="tier1 tier2 tier3"`

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

Commit messages:
 - Clean JDK-8317128: java/nio/file/Files/CopyAndMove.java failed with AccessDeniedException
 - Backport 36ac83904c9e81a01822b0e36ef677cae2808709

Changes: https://git.openjdk.org/jdk21u-dev/pull/863/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=863&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8073061
  Stats: 319 lines in 6 files changed: 307 ins; 3 del; 9 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/863.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/863/head:pull/863

PR: https://git.openjdk.org/jdk21u-dev/pull/863