It apparently broke clean builds, as the dependencies aren't in the project asset list or something anymore. I tried to fix this, but it seems impossible to do without relying on .NET SDK internals, as there's no point in the NuGet graph walk process that seems cleanly extensible.
Instead let's just do the much dumber thing: a bunch of .props files for content to import. Hooray!
This also means that I have to go through and *explicitly* disable transitive dependencies everywhere in RT. This thankfully isn't too hard.
Bans content from directly referencing Robust projects, instead it must go through new MSBuild items <UseRobustApi>. This way we can move types between RT projects without fear of causing breaking changes.
Robust.UnitTesting was both ALL tests for RT, and also API surface for content tests.
Tests are now split into separate projects as appropriate, and the API side has also been split off.
