RFR: 8324635: (zipfs) Regression in Files.setPosixFilePermissions called on existing MSDOS entries [v2]

[Eirik Bjørsnøs]

> Please review this PR to fix to a regression in ZipFileSystem, introduced by JDK-8322565 in PR #17170.
> 
> When `Files.setPosixFilePermissions` is called on an existing MSDOS entry, then `Entry.posixPerms` field will be -1 (all 1s in binary). The logic introduced by JDK-8322565 did not account for this and incorrectly sets the leading seven bits to all ones instead of all zeros.
> 
> The fix is to introduce a branch for `Entry.posixPerms` being -1 and deal with that case separately.
> 
> The PR adds a test case to `TestPosix` which reproduces the regression. While visiting this test, I also fixed an incorrect spelling of `setPosixFilePermissions` (also introduced by #17170).

Eirik Bjørsnøs has updated the pull request incrementally with one additional commit since the last revision:

  For clarity, add comments with the before/after zipdetails output of the relevant CEN fields

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Changes:
  - all: https://git.openjdk.org/jdk/pull/17556/files
  - new: https://git.openjdk.org/jdk/pull/17556/files/dabe0fb7..4bb77e1e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=17556&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=17556&range=00-01

  Stats: 22 lines in 1 file changed: 20 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/17556.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17556/head:pull/17556

PR: https://git.openjdk.org/jdk/pull/17556