Framework: Restrict combineReducers usage to data module

[aduth]

This pull request seeks to replace a reference to Redux's combineReducers in @wordpress/core-data with the equivalent utility exported from @wordpress/data. In so doing, it includes a new project-level ESLint syntax restriction to enforce this usage. The proposed benefit of this change is to ensure consistency, leverage performance benefits from #11255, and avoid bundling multiple copies of a combineReducers utility. Furthermore, the core-data package never defined an explicit dependency on redux and thus was only incidentally able to be built without errors.

Testing Instructions:

Ensure unit tests pass:

npm run test-unit

Ensure lint passes:

npm run lint-js

[youknowriad]

Good catch