support shinyWidgets textInputIcon input binding name

[bees4ever]

I work with many different form fields also like shinywidget and shinyfeedback is often in use. We use R/Shiny for an internal project of a big company and shinyfeedback is a big help. With this PR I want to add support for textInputIcon of shinyWidget. Maybe in the future there is more required. I would guess so.

Let me know what you need for this PR. You can see it in action here:

[bees4ever]

The newest changes actually also supports

shinyWidgets::numericInputIcon

[merlinoa]

Awesome thanks! this looks great. I'll review in the next couple days.