Add API for UntypedActorWithStash types

[ismaelhamed]

Added utility abstract classes for UntypedActors that support stashing:

• UntypedActorWithStash
• UntypedActorWithUnboundedStash
• UntypedActorWithUnrestrictedStash

Depends on #6325

Checklist

• This change follows the Akka.NET API Compatibility Guidelines.
• I have reviewed my own pull request.
• Changes in public API reviewed, if any.
• I have added website documentation for this feature.

[Aaronontheweb]

@ismaelhamed #6325 has been merged. I can start work on backporting it probably on Friday unless you want to do it (via git cherry-pick)

[ismaelhamed]

@ismaelhamed #6325 has been merged. I can start work on backporting it probably on Friday unless you want to do it (via git cherry-pick)

I think I can find the time to do it myself. I will be backporting #6323, #6325 and #6327 if you're fine with it.

[Aaronontheweb]

@ismaelhamed #6325 has been merged. I can start work on backporting it probably on Friday unless you want to do it (via git cherry-pick)

I think I can find the time to do it myself. I will be backporting #6323, #6325 and #6327 if you're fine with it.

Yes, that would delight me

[Aaronontheweb]

Is the general goal behind this API change to move away from the actor creation pipeline, so the stash is provided automatically as part of the base class infrastructure itself rather than injected in from the outside?

[Aaronontheweb]

LGTM

[ismaelhamed]

Is the general goal behind this API change to move away from the actor creation pipeline, so the stash is provided automatically as part of the base class infrastructure itself rather than injected in from the outside?

@Aaronontheweb If you think about it, using stashing is currently a little weird since users must implement an interface (including declaring the Stash property that, BTW, they are not instantiating themselves). That's because Scala traits can have behavior, which can't be done with interfaces in JAVA and CSharp (well, we have default interfaces now, but you get the point).

So, it is natural that these utility classes exist in the JAVA API, allowing the user to just derive from a class (like they would with normal actors) and get everything needed for stashing already set up. They can still implement the interfaces themselves if they choose to, but this is a bit of an improvement on the usability side.

[Aaronontheweb]

They can still implement the interfaces themselves if they choose to, but this is a bit of an improvement on the usability side.

Time will tell I guess, but I see your point.