Minecraft Version: 1.12.2
Inventory Tweaks Version: 1.63
This feature is very similar to touchscreen mode, except that it wouldn't conflict with the default, useful vanilla shortcuts, nor with mods' shortcuts (I.e., it would not be terrible) .
It's very annoying to click twice per item to pick it up and drop it in the inventory in the process of reordering the inventory. Wears down your mouse and your patience.
Click once on the item to pick it up, then releasing the button to release the item.