[Cocoa] Avoid some double-wrapping of strings and URLs

[Cocoa] Avoid some double-wrapping of strings and URLs
https://bugs.webkit.org/show_bug.cgi?id=123632

Reviewed by Anders Carlsson.

* Shared/API/c/cf/WKStringCF.cpp: Removed.
* Shared/API/c/cf/WKStringCF.mm: Copied from Source/WebKit2/Shared/API/c/cf/WKStringCF.cpp.
(wkNSStringClass): Added this helper.
(WKStringCreateWithCFString): If the passed-in CFString is already wrapping a WebString,
then retain it and return it.
* Shared/API/c/cf/WKURLCF.cpp: Removed.
* Shared/API/c/cf/WKURLCF.mm: Copied from Source/WebKit2/Shared/API/c/cf/WKURLCF.cpp.
(wkNSURLClass): Added this helper.
(WKURLCreateWithCFURL): If the passed-in CFURL is already wrapping a WebURL, then retain it
and return it.
* WebKit2.xcodeproj/project.pbxproj: Updated for renames.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@158456 268f45cc-cd09-0410-ab3c-d52691b4dbfc