After cbf1b4bc60bca3994b8f8685ee922e53a6b4eed2 the selected item got
deselected on Ctrl+Press, which made Ctrl+dragging a selected item
impossible.
Only deselect on Ctrl+Release. Add scenario to existing test case,
and update the documentation to clarify the properties involved, and
to point out that the event parameter might be nullptr.
Fixes: QTBUG-101647
Pick-to: 6.3 6.2
Change-Id: I749b1cb1a0a311f5c1d4c333984716f05f2c90b5
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>
Reviewed-by: Volker Enderlein <volker.enderlein@ifm-chemnitz.de>
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>
dfb4697e4a