[Development] QWidget mouse events - different order

[Rick Stockton]

QTBUG-25831 is re-opened, and assigned to me. The linked gerrit change
would "solve" the problem for Widgets- creating the issue that a LOT of
Qt5 modules are listening only for single-click, and would now need to
listen for both events if they need to respond properly to a big
sequences of fast single-clicking.

(Half of the "fast clicks" would now show as ButtonDblClick events, and
Qt5 would no longer provide corresponding clicks to for those modules to
"see".)
 Shawn Rutledge has suggested making the change configurable (see his
comment in the bug, he says it much better than I can paraphrase).

I feel, in contrast, that the ButtonDblClick should be always be
understood as a "real" event - a second mousebuttonpress which happened
very soon after the first, even though QT's recent history has done
otherwise. That of course implies that I am willing to patch 5.1 and 5.0
in the same way.

IMPORTANT: I have not solved for QML yet; only for widgets and (in
different bug QTBUG-35793), qtquick. They are going to handle mouse
events from QtGui in different modules, right?

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