When inserting a node into a parent, any live DOM ranges that reference
the parent may need to be updated. The spec does this by increasing or
decreasing the start/end offsets of each live range *before* actually
performing the insertion.
This caused us to crash with a verification failure, since it was
possible to set the range offset to an invalid value (that would go on
to immediately become valid after the insertion was finished).
This patch fixes the issue by adding special badged helpers on Range for
Node to reach into it and increase/decrease the offsets during node
insertion. This skips the offset validity check and actually makes our
code read slightly more like the spec.
Found by Domato :^)
