Introduce Visitor Identify API in Internal (Beta)

Description

Form uses VisitorIdentifyService to summon DefaultVisitorIdentifyProvider : IVisitorIdentifyProvider.
IVisitorIdentifyProvider provides the mechanism to create the cookie (cookie name, how to store data in the cookie value, ...), to track a visitor.

• Due to a change in Progressive Submit Info (new feature) and Visitor Identify API, cookie keys are changed.
• There is no code change for developers.
• Developers can implement IVisitorIdentifyProvider to create their own mechanism.

Side effect: The state in which visitors submitted Forms (in the previous version of Forms) is obsoleted.