Check IR invariants

[kyouko-taiga]

The IR is typed and relies on many other invariants for wellformedness. However, none of these properties are properly enforced in the current implementation. It would be good to have a procedure to check that all invariants are satisfied so that we can assert wellformedness after a particular phase.

It should be noted that the invariants that hold will depend on the "stage" of the IR. In particular, raw IR does not necessarily defines an end access for each start access. The invariant check should therefore be parametrized by the phase to ignore certain invariants.