Inter-pipeline Data Access about filament

[rachitnigam]

One thought that came up while talking to @sampsyo is that the @interface stuff is currently used to reason about two properties: the minimum safe initiation interval for inter-pipeline conflicts, and the minimum amount of time before a resource and be reused for intra-pipeline conflicts. If we could separate the two out, we could say that a Register that uses its prev port cannot be reused for the rest of the pipeline's execution. This has the benefit of returning the "sane" semantics of prev ports where they will always contain the value stored in the previous iteration of the pipeline