Simple inlining pass
- Callgraph analysis
- Inlining pass over whole module - runs inlining per function in rev. topo order of callgraph DAG
- Inlining within a function - doesn't support substituting dynamic constants yet, but this case is caught with a panic
- Modify a function to have a single return node - needed for inlining
- Fix bug in editor where added nodes are checked for mutability