[Feature Request] on_drag_modulate property for CtrlInventoryGrid

[etherealxx]

Currently, when an item is being dragged (still being held), the item (visually) exist both on the grid and on user's mouse.

Would be nice if we have an option to adjust the color of the item on the grid. Kinda like modulate property on CanvasItem. So user could either adjust the transparency of the grid item by adjusting the alpha slider (like most games, where the item on the grid is either transparent or disappear when the item is in the middle of dragging/being held), or maybe recoloring it into other color whatever the user like.

(I just noticed there is no signal to detect if an object is being dragged. Maybe add that one as well? The available signal currently are the one that detect the click (inventory_item_selected) and the drop (item_dropped). Nothing that detect the drag)