RFR: 8359830: Incorrect os.version reported on macOS Tahoe 26 (Beta)

[Jaikiran Pai]

Can I please get a review of this change which proposes to address the issue noted in https://bugs.openjdk.org/browse/JDK-8359830?

macOS operating system's newer version 26 (currently in Beta) is reported as a 16 by older versions of XCode. JDK internally uses the `NSProcessInfo` and `NSOperatingSystemVersion` APIs to identify the macOS version and set the `os.version` system property to that value. The current recommended version to build the JDK on macOS is XCode 15.4. The `NSOperatingSystemVersion` API on that version of XCode reports macOS version as 16 instead of 26.

The commit in this PR updates the JDK code to handle this mismatch and set the `os.version` appropriately to 26. This fix is similar to what we did with macOS BigSur when the macOS version 10.16 was meant to mean 11 https://bugs.openjdk.org/browse/JDK-8253702. 

The existing `OsVersionTest` has been updated for some trivial clean up. Existing tests in tier1, tier2 and tier3 continue to pass with this change. If anyone has access to a macOS 26 Beta, I request them to build this change and run `tier1` tests to help verify that there aren't any failures.

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Commit messages:
 - update test
 - 8359830: Incorrect os.version reported on macOS Tahoe 26 (Beta)

Changes: https://git.openjdk.org/jdk/pull/25865/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25865&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8359830
  Stats: 72 lines in 2 files changed: 34 ins; 13 del; 25 mod
  Patch: https://git.openjdk.org/jdk/pull/25865.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25865/head:pull/25865

PR: https://git.openjdk.org/jdk/pull/25865