Replicates QTabBar::tabSizeHint for desktop style. Not every style implements custom size hints for tabs, where it would just fall through to returning sizeFromContents as it is passed in, leading to tiny tabs.

BUG: 409390

Before (Breeze)

Before (Fusion, slightly broken, we might not take into account the vertical offset for inactive tabs?)

Before (Kvantum, hideous as usual)

Before (QtCurve, unusable)

After (Breeze, no change)

After (Fusion, more correct now, doesn't fall back to 2 * grid unit anymore)

After (Kvantum, even more hideous)

After (QtCurve, now mostly correct, not sure why the width is off)