QAbstractSlider: fix invertedControls having no effect for left/right keys

There was a comment in the code that said:

// It seems we need to use invertedAppearance for Left and right, otherwise, things look weird.

It's not clear what that was referring to, but in its current state,
a slider with invertedControls set to true will not behave as expected:
pressing the left arrow key will decrease its value instead of increasing it,
and vice versa for the right arrow key.

As stated in the documentation (and by its name), invertedAppearance only
controls the appearance of the slider, and not the effect of key events.

Remove the comment and use invertedControls instead.

Change-Id: I13296cbda9244413978ef0d7f0856065f74fd0bf
Fixes: QTBUG-25988
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>

Author: mitchcurtis

src/widgets/widgets/qabstractslider.cpp

@@ -829,7 +829,6 @@ void QAbstractSlider::keyPressEvent(QKeyEvent *ev)
             break;
 #endif
 
-        // It seems we need to use invertedAppearance for Left and right, otherwise, things look weird.
         case Qt::Key_Left:
 #ifdef QT_KEYPAD_NAVIGATION
             // In QApplication::KeypadNavigationDirectional, we want to change the slider
@@ -848,9 +847,9 @@ void QAbstractSlider::keyPressEvent(QKeyEvent *ev)
             else
 #endif
             if (isRightToLeft())
-                action = d->invertedAppearance ? SliderSingleStepSub : SliderSingleStepAdd;
+                action = d->invertedControls ? SliderSingleStepSub : SliderSingleStepAdd;
             else
-                action = !d->invertedAppearance ? SliderSingleStepSub : SliderSingleStepAdd;
+                action = !d->invertedControls ? SliderSingleStepSub : SliderSingleStepAdd;
             break;
         case Qt::Key_Right:
 #ifdef QT_KEYPAD_NAVIGATION
@@ -868,9 +867,9 @@ void QAbstractSlider::keyPressEvent(QKeyEvent *ev)
             else
 #endif
             if (isRightToLeft())
-                action = d->invertedAppearance ? SliderSingleStepAdd : SliderSingleStepSub;
+                action = d->invertedControls ? SliderSingleStepAdd : SliderSingleStepSub;
             else
-                action = !d->invertedAppearance ? SliderSingleStepAdd : SliderSingleStepSub;
+                action = !d->invertedControls ? SliderSingleStepAdd : SliderSingleStepSub;
             break;
         case Qt::Key_Up:
 #ifdef QT_KEYPAD_NAVIGATION