Add support for nested components (e.g. `Stack.Item`)

[kamilzyla]

If the reactElement() function supported nested components (e.g. being able to pass Stack.Item to name), it would be possible to implement wrappers for such components more cleanly.

[DivadNojnarg]

How did you proceed until now with those nested elements?

[kamilzyla]

@DivadNojnarg Here's an example showing how you can use Stack.Item from Fluent UI:

library(shiny)
library(shiny.fluent)

customFluentComponent <- function(name, js) {
  dependency <- htmltools::htmlDependency(
    name = name,
    version = "0", # Not used.
    src = c(href = ""), # Not used.
    head = paste0("
      <script>
        (jsmodule.CustomComponents ??= {})['", name, "'] = (() => {", js, "})();
      </script>
    ")
  )
  function(...) shiny.react::reactElement(
    module = "CustomComponents",
    name = name,
    props = shiny.react::asProps(...),
    deps = list(shinyFluentDependency(), dependency)
  )
}

Stack.Item <- customFluentComponent("Stack.Item", "
  const Fluent = jsmodule['@fluentui/react'];
  return Fluent.Stack.Item;
")

shinyApp(
  ui = Stack(
    Stack.Item("Item One", order = 2),
    Stack.Item("Item Two", order = 3),
    Stack.Item("Item Three", order = 1)
  ),
  server = function(input, output) {}
)