Our selection handling regressed about utopia

[seanparsons]

@maltenuhn

Slight correction, it's not so much the click per se, but the mouse up that triggers some selection (especially in the cmd modified version of that). That was definitely an intentional change at some point in history.

The getPreferredSelectionForEvent function is likely responsible for the change in behaviour relating to cmd-double-clicking which also prevents selection from changing when elements are overlapping.

Cmd-dragging explicitly protects against changing selection during the mouse up.

Questions:

• Do we want to operate with the axiom that whatever is highlighted will be selected on a mouse down (similarly for cmd mouse down)?
• Should we never change selection on mouse up?
• Should we have a way of locking selection from changing during an entire drag operation?