[UIK-2523][dropdown] Fix Tooltip singleton stretched to fullscreen width

[ksimanov]

Motivation and Context

Fixed Singleton Tooltip example stretched to full width of window.

Might affect Select and Dropdown components.

How has this been tested?

manually tested examples in documentation, that might be affected

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue).
• [ ] New feature (non-breaking change which adds functionality).
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected).
• [ ] Nice improve.

Checklist:

• [x] My code follows the code style of this project.
• [ ] I have updated the documentation accordingly or it's not required.
• [ ] Unit tests are not broken.
• [x] I have added changelog note to corresponding CHANGELOG.md file with planned publish date.
• [ ] I have added new unit tests on added of fixed functionality.