The Witness: Add info about which door items exist in the pool to slot data

[NewSoupVi]

Right now, slot data contains this info:

1. Every possible door item -> Doors it unlocks
2. Unlockable doors for which some item exists that unlocks them in this slot's itempool

This is not enough to identify, client-side, which door items exist in the itempool, because there are multiple door items that can unlock any given door, depending on options.

So, this replaces the "door hexes for which items exist in the pool" slot_data entry with "door items that exist in the pool". From this, "Unlockable doors for which some item exists that unlocks them" can be inferred (with the help of disabled_entities as well), and the appropriate change has been made client side.

This allows a new client side feature that displays in-game what item a door is locked by, which aids in hinting. It also should be a slight memory use reduction on average, as the amount of door items is always less than or equal to the amount of doors they unlock.

A new client release has been made to support the slot_data change. https://github.com/NewSoupVi/The-Witness-Randomizer-for-Archipelago/releases/tag/v6.0.0p9

[NewSoupVi]

Drafting because this solution is incompatible with https://github.com/ArchipelagoMW/Archipelago/pull/2916, where a door item might not open a specific door despite the door not being disabled

[NewSoupVi]

I now know how I want to solve the conflict, and merging either PR will (correctly) create a merge conflict on the other, so I'll leave both open.