Group up style information changes and report at the end of an op batch

Operation batches that modify a large number of paragraphs (or repeatedly modify the same paragraph) can cause numerous unnecessary style change events to be triggered. Rather than reporting these instantly, track them as they occur and emit the style change summary on batch end.

Related to #610.
The reason for the rename is that this is no longer responsible for actually updating the styles info. That is now done via the lazy property. This function is primarily about emitting the style state changes after a batch of operations has been completed.

I've left ``updateEnabledState`` alone because that still is responsible for immediately updating the internal state, and currently has no performance impact.