[ddc] Implement new runtime type system

[nshahan]

New type system is needed to support deferred imports and stateful hot reload.

Requirements:

• Type representation separate from class representation (types can be loaded separately from the class code)
• Modular compilation and loading (types can be added as needed when module loads)
• Support existing weak null safety with null safety warnings/errors modes.
• Update dwds to use new type system logic (before flipping the flag in ddc to enable new type system)
  Update dwds for new DDC type system webdev#1949