Centralized StyleCop version in Directory.Build.props.

[azchohfi]

Fixes #3187

Also removed ruleset files in favor of .editorconfig.

PR Type

What kind of change does this PR introduce?

• Code style update (formatting)
• Refactoring (no functional changes, no api changes)

What is the current behavior?

Multiple versions of StyleCop and unused ruleset.

What is the new behavior?

Single version of StyleCop and migrated away from ruleset files.

PR Checklist

Please check if your PR fulfills the following requirements:

• Tested code with current supported SDKs
• Pull Request has been submitted to the documentation repository instructions. Link:
• Sample in sample app has been added / updated (for bug fixes / features)
  • Icon has been created (if new sample) following the Thumbnail Style Guide and templates
• Tests for the changes have been added (for bug fixes / features) (if applicable)
• Header has been added to all new source files (run build/UpdateHeaders.bat)
• Contains NO breaking changes

[ghost]

Thanks azchohfi for opening a Pull Request! The reviewers will test the PR and highlight if there is any conflict or changes required. If the PR is approved we will proceed to merge the pull request 🙌