MainWindowViewer::keyPressEvent()'s custom matching of these shortcuts
does not leverage all the features of standard Qt shortcut matching. As
a result, the corresponding actions cannot be triggered when their
assigned shortcuts consist of a single Latin letter without modifiers
and e.g. Ukrainian keyboard layout is active.
Furthermore, some key presses (e.g. Scroll Lock in my customized
keyboard layout) set QKeyEvent::key() to 0, which the custom matching
considers equal to an unassigned shortcut. So an action without shortcut
is triggered by such a key press.
Adding these 3 actions to MainWindowViewer and connecting the
corresponding slots to their triggered() signals allows to remove the
custom matching code and thus eliminates both of its issues.
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