Added Unicode support for new charts

[kalutkaz]

Pull Request description

Moved tooltip processing logic from the model to a separate class.
Added convert Unicode into symbols in legend and tooltip for new charts.

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General checklist

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• The milestone is specified and corresponds to fix version.
• Description references specific issue.
• Description contains human-readable scope of changes.
• Description contains brief notes about what needs to be added to the documentation.
• No merge conflicts, commented blocks of code, code formatting issues.
• Changes are backward compatible or upgrade script is provided.
• Similar PR is opened for PE version to simplify merge. Crosslinks between PRs added. Required for internal contributors only.

Front-End feature checklist

• Screenshots with affected component(s) are added. The best option is to provide 2 screens: before and after changes;
• If you change the widget or other API, ensure it is backward-compatible or upgrade script is present.
• Ensure new API is documented here