Make ScenrioContex.Stopwatch public

[mate1213]

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue).
• [X] New feature (non-breaking change which adds functionality). Feature Request
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected).
• [ ] Performance improvement
• [ ] Refactoring (so no functional change)
• [ ] Other (docs, build config, etc)

Checklist:

• [ ] I've added tests for my code. (most of the time mandatory)
• [X] I have added an entry to the changelog. (mandatory)
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.

I'm not shure this change require any additional test, or documentation. If so please make a comment, where should I put them and I will. THX