Better htmlwidget support

[thomasp85]

Fix #1034

This PR adds proper htmlwidget support for notebooks and inline quarto content. It follows suggestion 2 from @jmcphers and inlines the html directly, like the IRKernel. The reasons for this is mainly that supporting Jupyter Widgets would be a substantial addition with no user-visible upside since the one thing it provides (bidirectional communication) isn't possible with htmlwidgets anyway. If a compelling use case for bidirectional communication comes up we can revisit it.

We don't need pandoc or any other heavy dependency because the html is trivial to construct.

One wrinkle is that IRKernel defaults to deduplicating html dependencies from consecutive cells. This facility also exist in this PR but since Positrons notebook view renders each cell in isolation. Due to that the default for ark is to not deduplicate.

All changes only has an effect for notebooks. The standard path for viewer/plot pane remains unchanged

[DavisVaughan]

The code all seems good, but i have not actually been able to get this feature to work for me yet

Ping me on slack if the examples below (i.e. leaflet) work for you and we can try to figure out what I'm doing wrong before merging

[DavisVaughan]

Is this supposed to work?

library(leaflet)
m <- leaflet() %>% addTiles()
m

I tried it in a qmd with inline output turned on and got a blank output pane

[DavisVaughan]

another one that doesn't work for me

library(billboarder)

# data
data("prod_par_filiere")

billboarder(data = prod_par_filiere) %>%
  bb_barchart(
    mapping = aes(x = annee, y = prod_hydraulique),
    color = "#102246"
  ) %>%
  bb_y_grid(show = TRUE) %>%
  bb_y_axis(
    tick = list(format = suffix("TWh")),
    label = list(
      text = "production (in terawatt-hours)",
      position = "outer-top"
    )
  ) %>%
  bb_legend(show = FALSE) %>%
  bb_labs(
    title = "French hydraulic production",
    caption = "Data source: RTE (https://opendata.reseaux-energies.fr/)"
  )