Feature Request: full gif support

[carlos-pusch]

Hi @GuangchuangYu ,

at first great work. Thanks for this helpful library!

The geom_image function works perfect with svg files, but unfortunately there appears an "error" when a gif image is used.
Only the first image is displayed, even if the package gganimate is used to create gifs with a plot.
I understand that a gif file is based on multiple images, and the first image displayed might be sufficient, but I need the full animation.

Is there a way to add the support of a full gif animation?
If this is possible, I would be very happy about an implementation.

Greetings

# R 4.2.1, Windows 10

x_x <- data.frame("V1"=1:3, "V2"= (1:3)^2, "type"=c("a", "b", "b"))

x_y <- ggplot() +
  geom_point(data=x_x, aes(V1, V2)) +
  ggimage::geom_image(data=x_x, aes(V1, V2, image='Sample.gif'))

x_y

x_z <- x_y +
  gganimate::transition_states(
    type,
    transition_length = 2,
    state_length = 1
  )

x_z

# sample gif: