Feature Addition

[copybara-service]

Feature Addition

Implement External Nodes for Groups

This commit introduces the concept of external nodes to Groups.
It allows a node in the parent graph to be connected to a node
in a group without having to include the external node in the group itself.

The main changes are:

• External Target: The External target provides a Map<string, { nodes: string[], point: Point, type: 'in'|'out' }> for each Group
• internalEdges input in the Graph: This array is used to provide the edges that are connecting the Group with external nodes
• Rendering logic: The external target node is rendered with a default proxy node template.
• Rendering logic: The edges between the external nodes and internal nodes are rendered.

This feature enable the following:

• Connect a Node in the main DAG to a Node in a Group without having to declare the node in the Group
• Connect a Group with external Nodes
• Keep a consistent look for the group.
• Create complex diagrams using subgraphs.
  Limitations
• If two nodes are in different groups or have a parental difference of more than 1 then we can't show edges between them yet.
• This feature currently works in layout direction left to right or right to left, while using layout top to bottom or bottom to top there is some shifting in x axis of the node

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