kstyle: Properly align text in ToolButton with icon

Sometimes button labels in a ToolButton without icon and a ToolButton
with icon are not vertically aligned even if all buttons have the same
height. This is caused by double-to-int.

The original top padding `(contentsRect.height() - textSize.height()) / 2`
can be rounded down, and when the padding is rounded down, so
`contentsRect.height() - padding - textSize.height() ≠ padding`.

After this change, textRect is calculated based on the remaining space.

For example, `contentsRect.height() = 32`, and `textSize.height() = 15`,
so the padding is 8. Before this commit, the bottom padding will be
`32 - 8 - 15 = 9 ≠ 8`. After this change, the bottom padding is the
same as the top padding (8), so the visual glitch is fixed.

kstyle/breezestyle.cpp

@@ -4647,8 +4647,9 @@ bool Style::drawToolButtonLabelControl(const QStyleOption *option, QPainter *pai
                 iconSize);
         }
 
-        textRect = QRect(QPoint(iconRect.right() + Metrics::ToolButton_ItemSpacing + 1, contentsRect.top() + (contentsRect.height() - textSize.height()) / 2),
-                         textSize);
+        const int padding = (contentsRect.height() - textSize.height()) / 2;
+        textRect = QRect(QPoint(iconRect.right() + Metrics::ToolButton_ItemSpacing + 1, contentsRect.top() + padding),
+                         QPoint(contentsRect.right(), contentsRect.bottom() - padding));
 
         // handle right to left layouts
         iconRect = visualRect(option, iconRect);