added macos implementation

[riccardo-lomazzi]

✨ What kind of change does this PR introduce? (Bug fix, feature, docs update...)

This commit introduces the MacOS implementation for the plugin.

⤵️ What is the current behavior?

Currently the MacOS integration isn't included.

🆕 What is the new behavior (if this is a feature change)?

Now it uses the same location services as iOS (complete with MacOS version availability checks) to provide geolocation.

💥 Does this PR introduce a breaking change?

No.

🐛 Recommendations for testing

📝 Links to relevant issues/docs

Creating a macos plugin also automatically created stub files for the other platforms implementations, e.g kotlin files in the android folder. These files can be safely removed.

🤔 Checklist before submitting

• [ x] I made sure all projects build.
• [x ] I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy.
• I updated CHANGELOG.md to add a description of the change.
• [x ] I followed the style guide lines (code style guide).
• [x ] I updated the relevant documentation.
• [ x] I rebased onto current master.