Refactor DiffStatus into a class

DiffStatus is a class that exposes constants and member functions.
AbiDiffHelper calls the member functions to determine how to report the
diff. The actual value of a DiffStatus object is encapsulated so that
developers can define new status without changing existing logic.

Test: ./test.py
Bug: 259148872
Change-Id: I2c3be62046aa01d68c84690cb158f8fc7a5b474b
4 files changed