Write passes for doing more advanced data access analysis

[hansihe]

We have the ability to easily do much more granular change tracking than simple assigns level like LiveView does.

I imagine an assign_in which, when given a path, will update something more deeply nested in the assigns.

We can persist that change information and use that as a first level of change tracking.

When combined with #12, this could enable us to do some really impressive optimizations.