RFR: 8352480: Don't follow symlinks in additional content for app images [v4]

[Alexander Matveev]

> - Symbolic links will not be followed for `--app-content` on all platforms.
> - Added test to cover this case.
> - `MacHelper` updated to use "cp -R" instead of "cp -r" when unpacking DMG, since "cp -r" on macOS is not documented option and when used `cp` will follow symbolic links which breaks test. "cp -R" does not follow symbolic links.

Alexander Matveev has updated the pull request incrementally with one additional commit since the last revision:

  8352480: [macos] Don't follow symlinks in additional content for app images [v6]

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Changes:
  - all: https://git.openjdk.org/jdk/pull/24974/files
  - new: https://git.openjdk.org/jdk/pull/24974/files/166c3ffa..5c8dc6d8

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=24974&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=24974&range=02-03

  Stats: 56 lines in 1 file changed: 23 ins; 2 del; 31 mod
  Patch: https://git.openjdk.org/jdk/pull/24974.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24974/head:pull/24974

PR: https://git.openjdk.org/jdk/pull/24974