Change c12072c685 fixed a problem
where tab labels would overlap with the icons if the tab became
too small to contain the text. But it did not properly account
for the full area occupied by the icon, because the horizontal
padding is hardcoded to 4 in the mac style, whereas in the
common style (where the icon is drawn) it uses the pixel metric
for this.
In addition, the change only allocated space on the left side,
causing the label to no longer be centered.
Task-number: QTBUG-61235
Change-Id: Ieec4f7044584361f92045addbc8bbd81bd5c9fc7
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@qt.io>