it already needs to locate the correct pair anyway to know the left/right for DoubleChestInventoryWindow, so we might as well use this logic for initializing the DoubleChestInventory itself too. The old logic in tile/Chest didn't work correctly.
this unblocks a variety of changes, such as positionless tiles, enhanced APIs on Blocks for inventories, and also eliminates a bunch of cyclic references within the core code.
linked to #5033
the intent of these hacks was to break cyclic references to avoid having objects lingering in memory. However, all of the stuff that's being removed in this commit no longer has any effect anyway, due to the fact that these things don't circularly reference each other anymore. Notably, Tile inventories now keep Position instead of a Tile ref.
in pretty much every case, these usages really wanted to read the tag's contents anyway, which can be combined with a getTag() and instanceof call for more concise and static analysis friendly code.
In the few cases where the tag contents wasn't needed, it still wanted to check the type, which, again, can be done in a more static analysis friendly way by just using getTag() and instanceof.
this allows multiple problems to be solved:
1) Cycle between tile and inventory is now removed.
2) BlockInventory now provides a consistent API for plugins to get the block holding an inventory.
