Gwenview's {nav Operations} sidebar uses custom `QToolButtons` which are
wide and left aligned. Special support for this in Breeze was added with
2fb62271d777. However with the transition to KF5 something broke: While
the alignment to the left still worked, there was not enough space
between the left button border and the icon:
{F5539728}
This is fixed by adding the appropriate margin:
{F5539730}
Note how this replicates exactly the spacing of the toolbuttons in the
regular toolbar on the top (which had its icon size set to "small" in
this screenshot).
CCBUG: 381535