Rewrite inventory transaction system to an instruction-based model (like ItemStackRequest) instead of slot-change model (legacy)

[dktapps]

Description

ItemStackRequest was implemented as a shim on top of our existing InventoryTransaction API to get the benefits of the new protocol without BC breaks for plugins.

However, since the ItemStackRequest protocol includes a ton of information that the old system didn't, we can build a new API that exposes this information to plugins.

Since the old system focused on slot changes (old/new), it didn't provide any way to track movements of an item, which is something plugin devs want to know about frequently. The new system is instruction-based rather than just "change this slot to this thing".

Make no mistake: This is a big project that will likely take a lot of time and effort to complete. The concept is fundamentally different from the legacy system.

Justification

Improve plugins' ability to understand what players are doing to inventories