Move to a more granular model with reified state functions associated with edges.

Major differences over old "new l3 adjacencies" algorithm:
- add nodes for L2 interfaces instead of overloading physical interfaces
- split L3 interface into bridged and non-bridged variants
- support multiple tag-handling l2/l3 interfaces on the same physical interface
- allow multiple bridge domains per node
- use typed edges between nodes, where each edge contains a state function
- restrict the type of operations that can be performed on each edge type

Other notable features:
- disable each interface with subinterfaces that allow overlapping input tags
- add modeling support for individual trunk interfaces attached to multiple bridge domains
- Add InterfaceTopology to each interface encompassing tag-handling and bridging configuration
  - Must be populated prior by end of conversion
  - Add legacy helpers to populate interface topology for existing vendors
  - Replaces switchport/encapuslation settings as source of truth for behavior
    - Existing settings preserved as informational