Native background render node

[adamgerhant]

Creates a network to render the node graph UI with the generate_node_graph_overlay_network function. Does not include a runtime or system for evaluating a network, which is currently achieved by https://github.com/GraphiteEditor/Graphite/pull/3129

depends on https://github.com/GraphiteEditor/Graphite/pull/3122

Note: This branch is very buggy due to various rebases and structural changes. See #3159 which fixes these issues

[Keavon]

!build