Expose `delete` as a direct dsc resource operation

[SteveL-MSFT]

Summary of the new feature / enhancement

It may be simpler for DSC resource implementations to implement delete rather than have logic as part of set to handle _exist. We can still support _exist as a special keyword in configuration where dsc knows to call delete if implemented.

PowerShell resources already implement ensure differently, so that won't change either way.

Proposed technical implementation details (optional)

No response

[michaeltlombardi]

I'm not sure about this - it does move a little bit away from the underlying state management model of an instance + properties - if you have delete, why not create (don't update if exist) or modify (don't create if not exist)?

It seems like the sort of thing I might expect a higher order tool to implement, rather than a resource or DSC itself.

[SteveL-MSFT]

@michaeltlombardi the idea is that this can simplify resource authoring as you can have clear separation of set (CreateOrUpdate) and delete whereas, for example, in the registry resource, I basically have a bunch of if statements to check if _exist is passed in and it would simplify the code by having delete a separate code path. For end users, they can call delete directly via dsc resource delete ..., but if using config, it would be abstracted so deletes can occur with create/update within the same config.

[SteveL-MSFT]

We should allow resources to implement _exist directly, but if the resource implements delete then dsc will use that to handle _exist rather than passing that to the resource.

[SteveL-MSFT]

Discussed with @mgreenegit and we agreed to move forward with this proposal