[Tracking] Support for graphs (node-link diagrams)

[grtlr]

This will touch various areas of Rerun so we will split the work up over multiple PRs. This PR is a living document and will be updated to reflect the current status of the implementation.

Must-haves for the initial release

Corresponding PR: #7500

• Support graphs in the Rerun data model
• Enable styling of nodes through the Rerun SDK
• Ensure proper bindings for all languages
• Create Python example for logging graphs
• Remove experimental feature flag
• Add archetypes to gen_common_index.py
• Deal with unused lint warnings for things that we need in the future
• Fix codegen problem related to GraphType
• Add icon for graph view in the UI
• Create datatype::StringPair and switch GraphNode to Utf8
• Update Python example for Utf8Pair
• Use VisualBounds in Viewer Properties
• Fix binary tree example
  • Implicit nodes are currently on an escape trajectory.
  • Add entity_offset_x to C++ and Python examples
• Entity rect box is drawn incorrectly
• Fix lattice example (remove positions in Python and C++)

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Future work

We will tackle the following things after #7500 lands.

Data Model

• Make the nodes draggable in the view #7916
• Enable styling of edges through the Rerun SDK (blocked by Tagged components #6889)
• Enable linking accross entities, potentially using a <entity_path>#<node_id> convention. (Allow linking of GraphNodes across different entities #8162)
• Support (statically) logging two archetypes to the same entity (Panic due to assertion chunk_id_removed.is_some() #7992).

Graph Layout & Viewer

We decided to start with implementing force-based layouts, because they support a wide variety of use cases and allow dynamic/temporal graphs out of the box.

• Support of external layout algorithms through the positions: Position2D component (closed by Implement graph components and archetypes #7500)
• Investigate other layout options in the Rust ecosystem (fdg, layout-rs, graphviz-rust). All of them have some shortcoming for our use cases.
• Re-implement force-based layout from d3-force. (⌛ Ongoing)
  • Implementation currently lives here: https://github.com/grtlr/fjadra, but will likely change to Rerun org.
  • Re-implement d3-quadtree to enable Barnes-Hut approximation 🏎️
  • Implement PositionX and PositionY force
  • Implement Collide force
  • Implement ManyBody force
  • Implement remaining forces 🦉
• Allow dynamic configuration of forces through blueprints

Examples & SDK

• Create C++ example for logging graphs
• Use ProjectDirs to pull in datasets for examples (social graph; Observable)
• Implement external data loader for GraphViz files #8159