Hey I went through the code the initial work looks good, however I've found some points I would like to see added / changed:

For the Stage.ts:

• Set the default boundsMargin of the stage when creating the rootNode.
• Add getter/setter for boundsMargin on Stage and have it also adjust the boundsMargin of the rootNode.

For the CoreNode:

• for get boundsMargin I don't think we need to check if the boundsMargin in the props is an Array or not, just check if this.props.boundsMargin is not null and return that value. If it is null let it check the parent node(s) with the changes to Stage we won't need the stage.boundsMargin
• In case the boundsMargin for a CoreNode is set upon creating the node we should call the boundsMargin setter like we are doing with the shaders/texture (line: 761)

LGTM