Convert Configurable.AddPostProcessor to take an interface

Configurable.AddPostProcessor takes a function pointer and stores
it in the Configurable.  This makes any property struct with a
Configurable that has AddPostProcessor on it not cacheable.

Take an interface instead so that the type that implements the
interface can be  hashed.

Test: TestPostProcessor
Change-Id: I89065787ebd8658e5f4c71ef5ac49301a4760cd0
2 files changed