fix: Start migrating encodePassable and rankOrder from agoric-sdk to endo

[erights]

For our passable data types, mostly, we have a clean abstraction layering between the "marshal" layer (here in the endo repository) and the "store" layer (currently in the agoric-sdk repository). However, two modules (rankOrder and encodePassable) currently at the store layer really belong at the marshal layer.

The encodePassable API and marshal's encodeToCapData and encodeToSmallcaps APIs have converged to the degree that they should. They can be understood together. Before smallcaps, I originally wanted to do this in the hope that encodePassable would become an alternate to capData for general use, but @warner 's criticisms below are likely fatal. The remaining purpose of encodePassable is specialized uses for which a sort-order-preserving string encoding is useful. Nevertheless, because of the conceptual similarity and layering, it is clearer for these to live here.

See also Agoric/agoric-sdk#4435 which we should make progress on as part of a larger project to explain these two abstraction levels and how they relate.

See also Agoric/agoric-sdk#6260 for keeping these two in sync until the situation simplifies.

[kriskowal]

I’m excited to see this move up and generally excited about separating the JSON/binary representation layers. I also see a lot of similarity to Syrup in this binary encoding. Similar but not the same, of course.

I can give this a closer read when it gets higher in priority.

[gibson042]

I've made it through encodePassable.js, and will come back later for rankOrder.js.

[gibson042]

I feel most strongly about PassStyleRankAndCover being out-of-place in rankOrder.js (at least while it hard-codes prefix sigils from encodePassable.js), but everything appears like it will function correctly. I support merging now or fixing first, whichever is least disruptive to the relationship between endo and agoric-sdk.