[#1465, #1771, #1774] Add ability to move advancements from one item to another

[arbron]

This adds a few tools to improve the usability of advancements, specifically to aid in the process of adding advancements to an item that is already on a character sheet.

This adds the ability to use drag-and-drop to copy a single advancement from one item to another. It also allows for dragging an entire item onto the Advancement tab of another to copy all advancements over. Regardless of which method is used, the system will check to ensure that each advancement doesn't already exist on the target (by comparing IDs) and that it is valid (only one Hit Points Advancement allowed). If the whole item is dragged over, it will display a prompt to give users an option of only copying over certain advancements.

If the item the advancements are being copied onto is embedded, the system will then show the Advancement Manager to apply any new advancements.

In addition, deleting an advancement from an embedded item will now unapply that advancement before deletion.

Resolves #1465
Resolves #1771
Resolves #1774

[akrigline]

likely to conflict with #1766 because we're both adding dragDrop to ItemSheet
I'd recommend splitting your drop handling of Advancement Data into a method dedicated to that _onDropAdvancement to mitigate those conflicts.

I'd also recommend the switch way of handling which method to call as it's more extensible.

[Fyorl]

Looks good to me, only minor suggestions, and one point of clarification: Where we talk about 'migrating' advancements here, we mean manual, UI-based migrations with users dragging and dropping individual advancements or advancement-containing-items onto other items? We're not attempting to perform automated migrations on users worlds at all?

[arbron]

Looks good to me, only minor suggestions, and one point of clarification: Where we talk about 'migrating' advancements here, we mean manual, UI-based migrations with users dragging and dropping individual advancements or advancement-containing-items onto other items? We're not attempting to perform automated migrations on users worlds at all?

This PR is just for manually dragging advancements to an item.

Fully-automated migrations on advancements aren't going to be possible because they require per-player action, but I was thinking we could implement a system in the UI to notify players that there are new advancements available and make it easy to apply them. That feature if we decide to implement it will be built on this foundation.

[Fyorl]

This PR is just for manually dragging advancements to an item.

Fully-automated migrations on advancements aren't going to be possible because they require per-player action, but I was thinking we could implement a system in the UI to notify players that there are new advancements available and make it easy to apply them. That feature if we decide to implement it will be built on this foundation.

That makes sense, thanks, just making sure I understood the context.