InterTypes Refactor

[p-stokes]

Roadmap to finish line:

• [x] Update DiagrammaticEquations.jl to use and export intertypes: relevant PR is https://github.com/AlgebraicJulia/DiagrammaticEquations.jl/pull/11
• [ ] Create ASKEMDeca in this repository in that uses the exported intertypes from DiagrammaticEquations
• [ ] Copy .it files and associated generated python for DecaExpr, SummationDecapode, and ASKEMDeca to the relevant PR