Discovery optimizations

[SteveL-MSFT]

Summary of the new feature / enhancement

Current design always performs a complete discovery, this will need to be changed with the following proposed optimizations:

1. When using dsc resource get -r <resourceName> if the is found, we don't continue with discovery.
2. If a config is provided, if a resource provider isn't used, don't call it to do discovery

Proposed technical implementation details (optional)

No response

[michaeltlombardi]

A future, but related enhancement - it would be useful to cache resource lookups and reuse the cache (or specifically invalidate it with a command flag). I think caching is likely more useful for providers than for DSC itself, but I can definitely see that as being useful to some degree, especially if you have a lot of resources on a system.

[anmenaga]

Additional details that will make some scenarios (like when only using native resources) way faster:

1. resources search is used one dir at a time in %PATH%; if at some point all required resources are found -> abort the search and start the actual operation
2. In every directory from step1 first search native resources, and, if required resource not found, search resource providers in that directory.