[Request] Animation button: from only 'play' to 'play'/'pause'

Currently when you press 'play' in a plotly animation, you can't stop the animation. It would be nice to have a 'play' / 'pause' button (just like you when playing / pausing a video & thus including the accompanying play/pause icons). In that way people have more possibilities to interact with the animation.

In line with #1205 animation_button could look like:

# option 1 with labels
animation_button(label_play = "Go!", label_pause = "Stop!")

# option 2 with icons
animation_button(label_play = icon_play, label_pause = icon_pause)

# option 3 with icons (different parameters)
animation_button(icon = TRUE)

Start at the animation_button entry point and trace the existing play control for plotly animations. Determine how the control state and labels or icons are represented, then make the completed behavior support toggling between play and pause and verify both requested interaction states.