Store: Mutate editor store reference in middlewares application

[aduth]

Extracted from #5228

This pull request seeks to resolve an issue where side effects are ignored when dispatching to the registered editor store. Because middlewares are applied to the editor store in a non-mutative fashion, the editor module itself uses a different dispatch reference from external modules. Therefore, if an external module attempts to dispatch an action on the core/editor namespace which has a side-effect attach, the effect will not be triggered.

Testing instructions:

This was observed in #5228 where, after updating to use withDispatch, it was observed that triggering fetchReusableBlocks would not actually fetch the blocks because the effect behavior was not triggered.

[aduth]

Adding to 2.3 milestone, as I'm observing that this incidentally resolves an issue where edit-post effects are not being respected, meaning the meta box initialization does not initialize data and therefore is causing a post with meta boxes to always prompt when attempting to navigate away.