Set drag and drop anchor using mouse down position

The way drag and drop is implemented when moving items around in the inventory is incorrectly handled imo.

It currently uses the position the cursor was at when the minimum cursor movement threshold was reached which can result in grabbing the wrong item. This doesn’t affect every UI element, only the most important one.

If my cursor is over an item enough that it is highlighted and I click to begin a drag there should be no expectation that I could ever drag anything else.

Visual example