refactor(share_plus): use win32's RtlGetVersion instead of manual lookup

[halildurmus]

Description

Simplifies the Windows version check in VersionHelper by replacing the manual lookup for RtlGetVersion API with the one provided by package:win32.

This also removes the redundant zero-initialization of all OSVERSIONINFOEX fields — calloc already zero-initializes allocated memory, so only dwOSVersionInfoSize needs to be set explicitly as required by the API.

Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I titled the PR using Conventional Commits.
• I did not modify the CHANGELOG.md nor the plugin version in pubspec.yaml files.
• All existing and new tests are passing.
• The analyzer (flutter analyze) does not report any problems on my PR.

Breaking Change

Does your PR require plugin users to manually update their apps to accommodate your change?

• Yes, this is a breaking change (please indicate that with a ! in the title as explained in Conventional Commits).
• No, this is not a breaking change.