QMacStyle: restore control size after re-initialization

We had to re-initialize NSSlider, due to some hidden problem with
stale geometry, when just setting properties of a cached control
(the remains of another previous QSlider render, using the same NSSlider).
But -initWithFrame: also resets the control size we set earlier,
thus 'small'/'mini' becoming 'normal'.

Fixes: QTBUG-107450
Pick-to: 6.4 6.2
Change-Id: Ice42c787ec65d89c1c15f9c89462b7804aafe51c
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

src/plugins/styles/mac/qmacstyle_mac.mm

@@ -432,7 +432,9 @@ static bool setupSlider(NSSlider *slider, const QStyleOptionSlider *sl)
     // NSSlider seems to cache values based on tracking and the last layout of the
     // NSView, resulting in incorrect knob rects that break the interaction with
     // multiple sliders. So completely reinitialize the slider.
+    const auto controlSize = slider.controlSize;
     [slider initWithFrame:sl->rect.toCGRect()];
+    slider.controlSize = controlSize;
 
     slider.minValue = sl->minimum;
     slider.maxValue = sl->maximum;