publicize container id

[DebitCardz]

Publicize the container id of a Window to primarily allow properly closing menus on the Bedrock Platform.
Bedrock has an issue where you cannot close a InvUI Packet Container because the Bukkit Player#closeInventory method cannot close the menu without a proper container id being specified, the only way to resolve this is to manually send the close container packet yourself with the container id attached so Bedrock Clients can properly close InvUI Menus

[NichtStudioCode]

The close packet with id 0 was not intentional. I've fixed this in 33f4d37, but let me know if there's still any issues with this / if this PR is still needed.

[DebitCardz]

I'm a bit busy until New Years, I'll let you know by then/a bit after

[ItWasEnder]

I beleive this field has no reason not to have a getter. Most if not all fields part of an api should have getters available and only setter should be private when nesssesary.

[NichtStudioCode]

I beleive this field has no reason not to have a getter. Most if not all fields part of an api should have getters available and only setter should be private when nesssesary.

No, exposing implementation details for no reason is bad API design. Also, as far as I know Bukkit doesn't expose container ids anywhere either.