missing background in xetex and fix RTL stuff in preview

missing background in xetex and fix RTL stuff in preview

* previwes with xetex did not produce any background (\pagecolor does not work for some reason), adding the direct command for that, \special{background <color>} inside the preview box solved it.

* similar to #12923 we should push the color node in horizontal mode

* there is a bug in preview with LuaTeX with main RTL language, this commit fix this bug, but it should be removed when it is fixed upstream (the code related to \pr@set@pagerightoffset)