Blender Git Loki

Fix T86867: Node Editor: Avoid deselect-all triggering on every box-
select

In 'Set/Replace' mode this is not a problem, but 'Extend' or 'Subtract'
modes were useless with the current behavior.
The problem here is that 'node.select' fires before 'node.select_box'
(which is fine) but deselects immediately on click.

This issue has come up before in other editors, see
{T70457}
{rB395dfff103e1}
{rBa8ea1ea1b7d5}

Now delay deselection in empty space to mouse release (same as done in
before mentioned report).

also related:
ref T57918
ref T63994

Maniphest Task: T86867

Differential Revision: https://developer.blender.org/D10801