valueBox arguments inconsistent

Both flexdashboard and shinydashboard have valueBox function, with similar arguments, in one we need to use icon = "fa-calendar" in the other icon = icon("calendar"), one has caption the other has subtitle, maybe harmonise them?

flexdashboard::valueBox(value, caption = NULL, icon = NULL, color = NULL, href = NULL)
shinydashboard::valueBox(value, subtitle, icon = NULL, color = "aqua", width = 4, href = NULL)

Related SO post
See example:

flexdashboard test.rmd

---
title: "My Icon"
output: 
  flexdashboard::flex_dashboard
---

```{r}
library(flexdashboard)
valueBox(42, caption = "my caption", icon = "fa-calendar")
```

Output:

shinydashboard

library(shiny)
library(shinydashboard)

ui <- dashboardPage(
  dashboardHeader(),
  dashboardSidebar(),
  dashboardBody(
    valueBox(42, "My Icon", icon = icon("calendar")),
  )
)

server <- function(input, output) { }

shinyApp(ui, server)

Output:

Start with the valueBox entry points in flexdashboard and shinydashboard, using the supplied test.rmd example and the comparable shinydashboard snippet to compare argument names and icon handling. Decide the harmonized API before changing it; done means the two valueBox interfaces behave consistently for the demonstrated caption/subtitle and icon use cases.