Move state sentinels into TypeFeedbackVector.

These sentinels were in the wrong place, living in only tangentially related class TypeFeedbackInfo, but they codify state in the TypeFeedbackVector.

R=ishell@chromium.org

Review URL: https://codereview.chromium.org/579153003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24037 ce2b1a6d-e550-0410-aec6-3dcde31c8c00