(bug 38545) Fix RTL position of the drop-down arrow
In RTL interface the drop-down arrow overlaps with the text.
The arrow was positioned explicitly in relation to the left margin, and this
can't work in a flipped RTL environment. I changed the position to "right"
and modified the arrow image a bit.
Some visual tweaks to the arrow may still be needed. Another option can be
to convert the image to SVG or to use a character like ▼.