feat: add fakeDurable option to assist durability conversion

[FUDCo]

This change adds a fakeDurable option to the makeScalaraBigFooStore and defineDurableKind/defineDurableKindMulti calls. Collections or virtual objects that result from using this option are not actually durable but will appear durable for purposes of being inserted into another durable collection or durable object. Note that such objects will not survive upgrade -- they will be discarded on upgrade like any other non-durable object -- but can be used in code that is in the midst of conversion from using purely virtual objects to durable objects. By relaxing the requirement for transitive durability, we hope to ease the conversion effort by enabling objects that will eventually be durable to be used as if they were durable even though they're not durable yet.

Closes #5454

[erights]

LGTM, thanks!!!!

[erights]

Amount of duplicated code here is unfortunate. If there's a way to consolidate without making other things noticeably worse, it's probably worth it.

[erights]

A bit surprising since collectionManager uses flags of exactly these two names but insists that those are mutually exclusive. I don't have a suggestion, so it you don't think of an improvement, you can leave this as is.

[warner]

This does what it says on the tin, so I'm ok with it landing.

But I'm not excited about this surviving in our codebase for very long: I'd like the companion ticket (about making it disabled by default) to consider removing it entirely once we've completed the durabilization transition. I'm hoping that future authors will be able to avoid the incremental conversion process.