Fix returning wrong client size for some controls in wxOSX

Make sure we are not neglecting the layout insets, for controls like
button, choice and gauge, otherwise client sizes became larger than
control sizes.

Closes #18717.

src/osx/cocoa/window.mm

@@ -3083,6 +3083,13 @@ void wxWidgetCocoaImpl::GetContentArea( int&left, int &top, int &width, int &hei
     {
         left = top = 0;
         GetSize( width, height );
+
+        int leftinset, topinset, rightinset, bottominset;
+        GetLayoutInset( leftinset, topinset, rightinset, bottominset);
+        left += leftinset;
+        top += topinset;
+        width -= leftinset + rightinset;
+        height -= topinset + bottominset;
     }
 }