Define helpers to inline IR objects from one component to another

[rachitnigam]

This is a problem that showed up when attempting #264 in #345: We need the ability to take a bunch of IR objects like expressions from one component and define the same ASTs into another component. The problem is that the leaf of these components are parameters which need to renamed to something that the new component understands.

This is something ir::Subst can almost do but it only allows you to do it in the same component. We need to define some methods on it to allow Subst and rewrite into another component. The approach is simple: copy the code from ir::Subst and define from_comp and to_comp to rewrite values from one component into another. Use the provided ir::Bind to remap the leaves.