ui tooltip keeps getting lower on each successive over

https://youtu.be/0WHT8OSSbPs

```
val d = container { solidRect(50, 50) }

val tooltip = d.uiTooltipContainer()

d.centerOnStage()

d.apply {
tooltip(tooltip, "hello world")
}
```

Run the Kotlin reproduction from the issue and observe the tooltip after successive mouseovers. Trace the tooltip positioning behavior used by uiTooltipContainer and tooltip; done means the tooltip stays at the intended position instead of moving lower on each successive hover.

Written by the indexing model from the issue text.