[headlesstools] Allow assembling when holding components on off-hand

[HectorCastelli]

Instead of using just floor-crafting for the blades, assembling could work when the handle is held on the off-hand.

In this case, a right-click interact could trigger the blade to be assembled and added to the player's inventory as the active item.

Alternatively, it might be easier to move the newly assembled item to the off-hand, move the handles to the inventory, and keep any left-over blades in the hotbar as-is.