MultiDefPrunedLiveness: add support for arbitrary uses/defs.
This now supports liveness holes within blocks where previously we
expected a phi def.
PrunedLiveness is streamlined for SSA liveness where we expect the
defs and uses to be related in the SSA def-use graph.
MultiDefPrunedLiveness was added on top of SSAPrunedLivenes to handle
extended SSA liveness that occurs with phis, but are still connected
in the def-use graph. Recently MultiDefPrunedLiveness was repurposed
for liveness of addressible storage. This means that we can now have
uses before defs in the same block without a corresponding phi.
Fortunately, handling this case is a straightforward extension of
MultiDefPrunedLiveness that does not complicate or penalize the
streamlined SSA case.
