Converting geom_tile's stroke

While this bug is "small", it is effecting heatmaply behavior so a fix would be very helpful.

Following is a reproducible example with the plots of ggplot2 and plotly:

df <- data.frame(
  x = rep(c(2, 5, 7, 9, 12), 2),
  y = rep(c(1, 2), each = 5),
  w = rep(diff(c(0, 4, 6, 8, 10, 14)), 2)
)
p <- ggplot(df, aes(x, y)) +
  geom_tile(aes(fill = w), colour = "grey50", size = 2) +
  theme_bw()
p


ggplotly(p)

ggplot2:

plotly (notice the grey borders are missing)

从 issue 中可复现的 R 示例开始，比较 ggplot2 和 plotly 的输出，重点关注 geom_tile 的颜色和大小设置。跟踪 geom_tile 的 ggplotly 转换入口；当灰色的图块边框像在 ggplot2 中一样出现在 plotly 输出中时，即表示完成。