feat(mat-tree): Get the parent tree node from child tree node

[stagefright5]

Feature Description

• MatTreeNode.parent should return the parent MatTreeNode

Use Case

• Useful while computing the node path
• Avoids multiple tree traversals

[zarend]

Hello @stagefright5 ,

Getting access to parent node from child is not prioritized at this time, but I'm going to convert this issue to a discussion.

-Zach