Consider making RID-agnostic marker tool package creation happen in more scenarios

### Is your feature request related to a problem? Please describe.
Today a user making RID-specific packages that are AOT'd has to call `dotnet pack` N + 1 times - where `N` is the number of platforms they would like to support. Then they must push those packages to a feed for usage.

This makes sense in the context of a scatter/gather, multi-machine CI build, where the goal is to produce the entire set of packages necessary to support all of the RIDs requested.

However, for inner-loop scenarios testing on a single machine, it is annoying to have to create the outer and inner tool packages via separate calls to `pack`.

### Describe the solution you'd like
We should consider either
* making the agnostic package _too_ when building the RID-specific packages
* supporting RID-less `pack` creating the subset of AOT-buildable packages in addition to the top-level package

While this could result in extra copies of the top-level package, each RID-specific build would be independently testable/usable on that RID with just a single invocation, and the top-level package copies should be identical.