Adding full as a valid parameter for the size arg in modalD…

[federiva]

Closes #4297
Hey! thank you for this awesome package. Adding a small feature for modals here.

How to test

library(shiny)
library(bslib)

shinyApp(
  ui = bslib::page_fillable(
    actionButton("open", "open modal")
  ),
  server = function(input, output, session) {
    observe(
      showModal(
        modalDialog("fullscreen!", size = "full")
      )
    ) |> 
      bindEvent(input$open)
  }
)

[CLAassistant]

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[gadenbuie]

Fullscreen modal sizes have a few flavors

Class	Availability
.modal-fullscreen	Always
.modal-fullscreen-sm-down	576px
.modal-fullscreen-md-down	768px
.modal-fullscreen-lg-down	992px
.modal-fullscreen-xl-down	1200px
.modal-fullscreen-xxl-down	1400px

I like that modalDialog() helps you find the appropriate value, but more and more I feel like throwing an error for invalid value unnecessarily breaks future-compatibility with changing sizes.

I think the behavior I'd prefer here in this case is:

1. If size is a known alias value, map to a specific class, e.g. "s" → modal-sm or "full" → modal-fullscreen.
2. If size doesn't already have the modal- prefix, prepend it, e.g. "sm" → modal-sm or "fullscreen-lg-down" → modal-fullscreen-lg-down

I'm going to bring this up internally to see what the rest of the Shiny team thinks before we move forward.

[gadenbuie]

Primarily to support Bootstrap size aliases (they use sm, md, lg, etc. instead of the s, m, l used here in size). If they know about the full class and use modal-fullscreen-lg-down we wouldn't prepend modal- to the class.

[federiva]

I like that! 🙂