Move padding/margin/offset writing mode logic from RenderStyle to LengthBox

Move padding/margin/offset writing mode logic from RenderStyle to LengthBox
https://bugs.webkit.org/show_bug.cgi?id=86970

Reviewed by Eric Seidel.

Move writing mode and bidi logic for paddings, margins and offsets from
RenderStyle to LengthBox. This way the same logic can be used for all
three removing unnecessary code duplication.

No new tests, no change in functionality.

* CMakeLists.txt:
* GNUmakefile.list.am:
* Target.pri:
* WebCore.gypi:
* WebCore.vcproj/WebCore.vcproj:
* WebCore.xcodeproj/project.pbxproj:
* platform/LengthBox.cpp: Added.
* platform/LengthBox.h:
* rendering/style/RenderStyle.cpp:
* rendering/style/RenderStyle.h:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@117832 268f45cc-cd09-0410-ab3c-d52691b4dbfc