Reviewed by Eric Seidel.

        JavaScriptCore GYP build should copy some headers into the target framework
        https://bugs.webkit.org/show_bug.cgi?id=55524

        After this patch, all the framework headers are exported as public
        headers.  We need to teach GYP how to handle private headers.

        I struggled to determine how to store the information about whether a
        header was public, private, or project (i.e., not exported).
        Generally, the GYPI should just list the files, but it seemed siliy to
        have an almost duplicated list of files in the GYP file itself.  If
        this design doesn't scale, we might have to revisit it in the future.

        * JavaScriptCore.gyp/JavaScriptCore.gyp:
        * JavaScriptCore.gypi:
        * gyp/JavaScriptCore.gyp:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@80094 268f45cc-cd09-0410-ab3c-d52691b4dbfc