Bugzilla

I'm repurposing this bug to cover the landing of a whole bunch of diagramming improvements from my hobby stack.  There's still some brainstorming on this bug that is potentially still relevant for potential future enhancements, but in particular, the patch stack in terms of this bug's stated purpose:
- Provides a concept of ontology mappings and ontology slots to teach the diagramming mechanism about various in-tree idioms like runnables.
- I think the concept of IPC piercing that comment 0 discusses may already have been landed by Jan 2023, but there are some further improvements to heuristics in this stack as long as we have the IPDL binding slot edges for those.  A more recent partial landing of my 2023 hobby stack improved the situation for us to have IPDL binding slots even in the face of the preprocessor, but I believe there may still be some more complicated pathological cases we don't handle.
- This implements hierarchical clustering and multiple potential axes for hierarchical clustering.
  - There are some incremental steps towards collapsing based on the hierarchy, but there's more to do. 
  - Bug 1776564 did get implemented/fixed to enable clustering by subsystem (`hier:subsystem`), but it's not the default.
- Additional improvements related to limit reporting, more granular overrides, and changes to the defaults and constraints have been implemented.

I'm repurposing this bug to cover the landing of a whole bunch of diagramming improvements from my hobby stack.  There's still some brainstorming on this bug that is potentially still relevant for potential future enhancements, but in particular, the patch stack in terms of this bug's stated purpose:
- Provides a concept of ontology mappings and ontology slots to teach the diagramming mechanism about various in-tree idioms like runnables.
- I think the concept of IPC piercing that comment 0 discusses may already have been landed by Jan 2023, but there are some further improvements to heuristics in this stack as long as we have the IPDL binding slot edges for those.  A more recent partial landing of my 2023 hobby stack improved the situation for us to have IPDL binding slots even in the face of the preprocessor, but I believe there may still be some more complicated pathological cases we don't handle.
- This implements hierarchical clustering and multiple potential axes for hierarchical clustering.
  - There are some incremental steps towards collapsing based on the hierarchy, but there's more to do. 
  - Bug 1776564 did get implemented/fixed to enable clustering by subsystem (`hier:subsystem`), but it's not the default.
- Additional improvements related to limit reporting, more granular overrides, and changes to the defaults and constraints have been implemented.
- Additional improvements to diagram metadata to support potential accessibility improvements.