[IR] Graph editor API

[justinchuby]

This design describes a stateful Editor api for editing ONNX graph structures. It provides an intuitive select and modify experience.

from onnxscript import ir

editor = ir.editing.Editor(graph)

Select

Users can select a part of the graph:

editor.select("node_a")
node_b: ir.None
editor.select(node_b)

editor.select_inputs(value1, value2)
editor.select_outputs(value3, value4)

Remove

editor.select(node_b)
editor.remove_selection(safe=True)

editor.select_inputs(value1, value2)
editor.select_outputs(value3, value4)
editor.remove_selection(safe=True)

Removing a subgraph and stich the connections.

For example

node_a -> node_b -> node_c  ==Remove(b)==> node_a -> node_c
node_a -> {node_b1, node_b2} -> node_c  ==Remove(b1,b2)==> node_a -> node_c

We need to analyze cases when the removal subgraph has multiple outputs and design a good default

Insert

The reverse of Remove

editor.select_inputs(value1, value2)
editor.select_outputs(value3, value4)
editor.insert(inputs, outputs, nodes)

Replace

editor.select_inputs(value1, value2)
editor.select_outputs(value3, value4)
editor.replace(new_inputs, new_outputs, nodes, safe=True)