Allow editors to set default review visibility

Is your feature request related to a problem? Please describe.
Currently reviews are not visible to authors, by default. They can be made visible on a case-by-case basis, and various parts (text box, custom review form answers, review files) can be made visible individually.

Describe the solution you'd like
An editor who has a business rule of sharing all reviews and review files with authors requested the ability to set default review visibility for completed reviews (except withdrawn reviews). In their words:

"I still think the current display signalling which reviews are visible to the author is a bit confusing. It would be good to have a single button making all available reviews (forms and .pdfs) visible to the author as a default, with the editor able to make some reviews invisible, rather than the other way around as it is now, with the editor having to check every single review for visibility. After all, reviews are for sharing with the author, by default. Many editors, myself included, forget to make one or more reviews available, leading to queries by the author. A single button making existing reviews (not those declined or withdrawn) available would be a great help."

Additional context
I personally am not sure where other editors stand on this. I'm putting in this issue as a proposal that we may or may not adopt.

No implementation files, tests, or entry points are identified. First clarify whether the proposal should be adopted and define the visibility rules for completed, declined, and withdrawn reviews; done should include an agreed editor workflow and corresponding coverage for review forms and files.