Refactor `Policy` inheritance

The following discussion from !23531 (merged) should be addressed:

• @dosuken123 started a discussion: (+5 comments)

  @godfat I have a question about class-level execution with inheritance. There is a super class OnlyPolicy that is inherited from Policy. All functionalities are inherited except class-level executions, such as strategy.., in this case.

  After I googled some, I figured out that we need to explicitly call self.inherited to load those things, but I wonder if there is a cleaner way in the realm of the ruby. Do you have any insights on this?