Batch mutations to PDOM elements

[zepumph]

From #1436:

Look into batching attribute setting to a single time per frame. (right now it is often based on model Properties, and may involve multiple, synchronous, DOM operations per frame. I'm not positive this is the case; it will need more investigation.

I think this would greatly help our performance in PDOM-heavy interactions. For example phetsims/ratio-and-proportion#356.

I'm not sure how hard it would be to create a space where ParallelDOM instances are marked as dirty, or even sections of it are marked as dirty. I'm nervous about this issue, because I think it could be pretty prone to regressions and destructive to implement. I will see if we want to devote time to this right now.