Convert PhetioIDUtils to an ES6 module

[samreid]

In phetsims/chipper#912 we discussed converting PhetioIDUtils to an ES6 module. PhetioIDUtils is not used in node, so this could be done right away. I see 22 or so HTML files referring to PhetioIDUtils.js", so this would be a significant amount of busywork. Not sure if it is worth the cost at the moment. Leaving unassigned.

[zepumph]

I'm not sure if this can happen without building the phet-io.js wrapper-side library with webpack. We want this global available in both frames, mostly to factor out logic.