Improve performance of calculating evolution trend metric value #19172

Description:

This will avoid calling Metrics::isLowerValueBetter each time the trend value for a row is calculated, which can be easily hundreds or thousands of calls depending on the datatable size.

refs L3-241

Review

• [ ] Functional review done
• [ ] Potential edge cases thought about (behavior of the code with strange input, with strange internal state or possible interactions with other Matomo subsystems)
• [ ] Usability review done (is anything maybe unclear or think about anything that would cause people to reach out to support)
• [ ] Security review done
• [ ] Wording review done
• [ ] Code review done
• [ ] Tests were added if useful/possible
• [ ] Reviewed for breaking changes
• [ ] Developer changelog updated if needed
• [ ] Documentation added if needed
• [ ] Existing documentation updated if needed