getCurrentOutputInfo() should be more cache aware

[cpsievert]

(Continuation of #3198 (comment))

Currently bindCache() doesn't consider getCurrentOutputInfo() when computing cache keys, but it probably should (especially considering that thematic implicitly calls it at plot time). For a minimal example of the suprising behavior it can lead to, run this app once to warm the cache), then change fg = "white" to fg = "red" notice how the fg of the plot remains unchanged (it should be red not white)

library(shiny)

shinyOptions(cache = cachem::cache_disk("./myapp-cache"))

ui <- fluidPage(
  theme = bslib::bs_theme(bg = "black", fg = "white"),
  "True foreground color",
  plotOutput("p")
)

server <- function(input, output, session) {
  output$p <- renderPlot(plot(1:10)) %>%
    bindCache()
}
thematic::thematic_shiny()
shinyApp(ui, server)

[cpsievert]

As a workaround, pass session$clientData$output_* to bindCache(), for instance:

output$p <- renderPlot(plot(1:10)) %>%
    bindCache(session$clientData$output_p_bg, session$clientData$output_p_fg)

Ideally bindCache() would do this automatically tho