Replace all internal usage of get_upstream with get_upstream_resource

[miscco]

We want to get away from raw resources, so prepare deprecation of it by replacing all internal usages

This PR relies on preparation in downstream repositories

[harrism]

Requesting changes to bake sure this doesn't merge before the downstream PRs are merged.

[harrism]

@miscco if you would like to merge this before downstream PRs, you could move the deprecations to a separate PR that won't be merged yet.

[bdice]

I'd favor splitting this PR into the new functions and then the deprecations, it does seem to help with moving the work along.

[miscco]

As far as I can see, there are two occurrences of get_upstream outside of rmm

rapidsai/cudf#15203
rapidsai/raft#2207

The only one I am not 100% sure how to get rid of is one other in raft where it explicitly checks whether a resource of of a given type, which is neither possible with the current resource_ref not is it desired

Given that those PRs are very small and limited in scope I believe we can wait a few days getting them in

[harrism]

Also the RMM Cython needs to be updated, and all uses of its current method.

[harrism]

@miscco does this PR also result in changing the semantics of MR equality as discussed in #1402 ?

[wence-]

Tiny doc nitpick.

[wence-]

Also the RMM Cython needs to be updated, and all uses of its current method.

We decided that this didn't seem to be necessary, since, for now, the Cython get_upstream function doesn't call into C++ (it returns a member variable of the cython class).

[miscco]

/merge