XForm "mat" versus "matrix" properties should be renamed

[tsherif]

Description of the problem

Xform nodes contain both mat and matrix properties. The difference is that mat contains the multiplied hierarchical transforms, whereas matrix contains the local transform of the node. This is unclear from the names (and led to this bug), so I'd suggest using more expressive names. Maybe localMatrix and globalMatrix?
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[xeolabs]

Agreed - I'll make it "localMatrix" and "modelMatrix".