Subtree cut/copy decision is made on action start instead of action end

[NooneAtAll3]

Steps to reproduce:

1. make a tree
2. click&hold a non-final node
3. drag to a final node
4. hold Ctrl
5. release the held subtree

Result: subtree gets moved

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This clashes with default behaviour in filesystem GUIs - you can drag files around, but whether file will be moved or copied (or made a shortcut of) gets decided by held buttons on release (which allows system to give indication on the action type that will be performed)