Add layer node chains, import/export edge connectors, and refactor graph editing to go thru a NodeNetworkInterface

[adamgerhant]

Closes #1892, closes #1891, closes #1893

Moves NodeNetwork to a private field and creates an API for modifying the network. This API contains the various functions for manipulating the network, automatically organizing it, and caching.

Todo

• Zoom to fit all is broken
• Add UI distinction between primary selection and all other selections
• Fix lock/hide icons
• Can't move layers
• Shift selecting multiple layers does not visually expand the selection box to include all layers.

Crashes

• If artboard is not a layer and a shape is drawn
• Deleting all nodes and a shape is drawn
• Moving layer to bottom of stack in layer panel
• Select layer, ctrl c, ctrl v, move layer, ctrl z, memory access out of bounds crash
• Toggling layer to node in nested network

Deferred:

• Move wire paths to Rust to fix disconnecting, display lines as vertical/horizontal
• Remove node_graph_to_viewport and derive with calculate_offset_transform from the node_graph_ptz.
• Automatically snap the viewport to keep export side bars aligned with the grid
• Add x offset for top of child stack (be able to move stacks left from their parent, but not overlap the wire)
• Automatically add nodes into chain if they are vertically aligned, within 3 spaces, and no additional primary outputs
• Only snap layers on the x axis when converting to stack position
• Store document metadata structure as transient metadata
• Fix deleting previewed nodes
• Add vec of network types to NodeNetwork, rather than storing type for each NodeInput::Network
• Drag selection in node graph runs document and checks for artwork intersections on every frame
• "To Artboard" has incorrect displayed types
• Node and wire culling in the graph
• Toggling layer to node which has an upstream chain breaks the graph.

[Keavon]

It appears to me that the color change for selected layers when either panel becomes the active or inactive panel isn't working anymore.

[Keavon]

Yet another Herculean development completed. You're on fire! This edited like 1/8 of our entire codebase 🤯. Way to go!