Redundant legend entries in facetted animations

MRE of a problem pointed out in #919

p <- ggplot(mtcars, aes(mpg, wt, color = factor(am))) +
  # works fine without frame
  #geom_point() + 
  geom_point(aes(frame = factor(vs))) +
  facet_wrap(~cyl)

ggplotly(p)

This also seems to be a problem for the non-ggplot2 approach:

library(dplyr)
mtcars %>%
  group_by(cyl) %>%
  do(
    p = plot_ly(., x = ~mpg, y = ~wt, color = ~factor(am), legendgroup = ~factor(am), frame = ~factor(vs))
  ) %>%
  subplot()

首先运行提供的 ggplotly 和非 ggplot2 MRE，以重现分面动画中的重复图例条目。跟踪 facets、colors、legendgroup 和 frames 的图例处理，然后验证两个示例都能生成非冗余图例，同时不破坏其动画或 subplot 行为。