Add helper function for converting a KeyedCodingValue to a CFTypeRef
https://bugs.webkit.org/show_bug.cgi?id=116461

Reviewed by Tim Horton.

* Shared/cf/KeyedCodingValueCF.cpp: Added.
* Shared/cf/KeyedCodingValueCF.h: Added.

* WebKit2.xcodeproj/project.pbxproj:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@150379 268f45cc-cd09-0410-ab3c-d52691b4dbfc