QCheckBox cannot be checked with plus (+) or unchecked with minus (-) key (Qt::Key_Plus / Qt::Key_Minus)

QCheckBox cannot be checked using the + key on the keyboard or unchecked using the - key on the keyboard when the widget is focused. As this is Windows default functionality (check the Properties on any file in the windows explorer and try it out with the read-only and hidden attribute checkboxes), our customers expect Qt's checkboxes to work the same.

Steps to reproduce:

• Build and launch qtbug89570.zip
• Note: The checkbox is not checked to begin with.

Plus key:

• Press +
• EXPECTED: Checkbox is checked.
• ACTUAL: Checkbox remains unchecked.

Minus key:

• Press the space key on the keyboard.
• Note: This toggles the checkbox state to checked and is necessary to demonstrate the minus key example as long as this bug is not fixed.
• Press -
• EXPECTED: Checkbox is unchecked.
• ACTUAL: Checkbox remains checked.

Note that neither the plus nor the minus key should toggle the state of the checkbox (like pressing space would). Plus only checks, minus only unchecks, that is pressing plus on an already checked checkbox does not change the state. Neither does pressing minus on an already unchecked checkbox.