geom_GeomContourFilled() not implemented in plotly

Hi,

Geom_contour_filled() is not supported by plotly.

Brief reproducable example below

library(ggplot2)

df <- tibble(x = c(0, 1, 2, 3, 4, 5, 0, 1, 2, 3, 4, 5, 0, 1, 2, 3, 4, 5, 0, 1, 2, 3, 4, 5, 0, 1, 2, 3, 4, 5, 0, 1, 2, 3, 4, 5),
        y = c(40, 40, 40, 40, 40, 40, 20, 20, 20, 20, 20, 20, 0, 0, 0, 0, 0, 0, -20, -20, -20, -20, -20, -20, -40, -40, -40, -40, -40, -40, -60, -60, -60, -60, -60, -60),
            z = c(52.25, 49.38, 48.31, 46.17, 44, 43, 45.75, 44.22, 43.19, 41.16, 40.2, 39.6, 40.13, 39.21, 38.26, 
              36.39, 36.2, 36, 35, 34.5, 33.65, 32.81, 32.6, 31.97, 31.25, 30.35, 30.3, 30, 28.5, 27, 26.62, 26.2, 25.99, 24, 21.5, 17.23))

# This works well
p <- ggplot(df, aes(x = x, y = y)) +
      geom_contour_filled(aes(z = z, fill = stat(level_mid))) +
  scale_fill_viridis_b()

# However it doesn't work with ggplotly:
ggplotly(p)

Warning message:
In geom2trace.default(dots[[1L]][[1L]], dots[[2L]][[1L]], dots[[3L]][[1L]]) :
geom_GeomContourFilled() has yet to be implemented in plotly.

Start by running the reproducible ggplot2 example and calling ggplotly(p) to observe the geom_GeomContourFilled() warning. Trace how ggplotly handles the contour layer; done means filled contours are supported without that warning and the example renders through plotly.