Fix comparison trends might be displayed incorrect for certain languages #18832

Description:

fixes #18802

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

@tsteur I have simplified the PR. The additional columns will now only be requested by the sparkline visualization and thus won't occur in any API output.

I've put it for now into 4.9. I had a quick look and it looks OK but I can't do a full review due to time. Be great for someone to do later a full review

This issue is in "needs review" but there has been no activity for 7 days. ping @matomo-org/core-reviewers

@diosmosis It seems the test I had added to this PR starts failing after https://github.com/matomo-org/matomo/pull/18761 has been merged in. The sparklines lost their color. See https://builds-artifacts.matomo.org/matomo-org/matomo/fixcomparisontrend/54586/Comparison_visits_overview_widget_sv.png

I guess the javascript method to initialize the sparklines is called before the colormanager, which is in Vue, has been loaded fully. The sparline requests contain "lineColor":[null,null]
Would you mind having a look and maybe pushing a fix on this branch?

@sgiehl that's weird, ColorManager is still in vanilla JS. I'll take a look.

@sgiehl should be fixed