Animate the torconnect icon to transition between connected states

As part of the work to add the new torconnect button to the browser chrome in #41608 (closed), I was thinking it might be cute to animate it out – i.e. transform the icon from its broken to normal state (without the oblique slash), and potentially include a color shift, before it automatically exits the toolbar.

@henry has looked into how the reload button works in Fx, and has dug up the following:

I looked into what firefox does for their reload and download-complete animations. Basically they create a single svg that contains all the 20px by 20px frames in a strip:

then they only expose one frame from the strip at a time and step-transform along it.

So we should probably do a similar thing if we want to animate the "not connected" to "connected" transformation.