Extend the per-frame-class bit we have to devirtualize IsLeaf to also
devirtualize IsFrameOfType. That is, move this data to FrameClasses.py.
This was done by going through all the frame classes, trying to preserve
behavior.
The only quirky thing is that I had to add two more trivial frame
classes, `nsAudioFrame` for audio elements, and
`nsFloatingFirstLetterFrame`. That's because these frame classes were
returning different answers at runtime, but they do this only on
conditions that trigger frame reconstruction (floating, and being an
audio element, respectively).
Differential Revision: https://phabricator.services.mozilla.com/D194703
c27730d3df