Splits from the position up to but not including the given parent without validation.
Should not be used directly. The "unsafe" part in this function only refers to the fact that the function does not do any validation, in contrast to primitives that always guarantee a schema-valid result on an unmodified blueprint.
Parent of the position from which to split
Offset of the position from which to split
Of Last Split
Node at which to stop splitting, this should be an inclusive ancestor of container, and will not be split itself.
Blueprint in which to perform the operation
Whether to move the position from which the split was started into the second half
The second half of the top-most node to be split, or null if no nodes were split.