Add command to list/sort by monomorphizations

[fitzgen]

• I want to be able to investigate monomorphizations of generic functions
  • list generic functions by the total code size of all of their monomorphizations
  • how many times was this generic function monomorphized?
  • how much space would I save if I switched to dynamic dispatch and trait objects for this generic function instead of monomorphization?

We can implement this by inspecting the demangled symbol for an IR node and extracting the generic function that it is a monomorphization of (if any) and storing that in the IR nodes as well. Then we would have a new analysis that groups IR nodes by the genric function they're monomorphizations of, and sort by most monomorphizations. Finally, we would expose it on the CLI as

$ svelte monos ...