`ggplotly` modifies values before creating tooltip

When drawing a geom_bar plot with negative values, a tooltip will display them as positive instead.

library(ggplot2)
library(plotly)
dataset <- data.frame(x = 1:2, y = 1:2 - 3, z = 1:2 - 3) # z == y
p1 <- ggplot(dataset, aes(x, y, z = z)) + geom_bar(stat = "identity")
ggplotly(p1, tooltip = c("y", "z"))

Even though y and z contain the same negative values, only z is displayed as negative in the tooltip:

This may be related to #560, #616 or #874. It was reported on StackOverflow here: https://stackoverflow.com/q/63862157/2554330

首先运行包含 geom_bar 以及 tooltip 字段 y 和 z 的可复现 ggplotly 示例，然后跟踪 ggplotly 在构建 tooltip 之前如何转换绘图数据。当 y 和 z 的负值保持为负数，并且在两个 tooltip 中显示一致时，即表示完成。