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

requested review from @aaronjc4

assigned to @rarbore2

mentioned in commit aa6760a0

merged