Project and package reference support

[alexrp]

Tracking issue for ProjectReference/PackageReference support.

[alexrp]

Goals:

• Managed projects should be able to reference Zig.Sdk projects.
  • Zig.Sdk projects should not be seen as managed (i.e. don't pass it to csc /reference:...).
  • Zig.Sdk projects must never be seen as RID-agnostic.
  • If the referencing project is doing a RID build, it should copy the output from the Zig.Sdk project to the root of the output directory.
  • If the referencing project is doing a RID-less build, it should copy the outputs from the Zig.Sdk project for all of its supported RIDs to runtimes/<rid>/native/ (tools/<rid>/native/ for an executable project) in the output directory.
    • This will require triggering multiple builds in the Zig.Sdk project.
• Managed projects should be able to reference Zig.Sdk packages.
  • This should Just Work since native libraries are packed into runtimes/<rid>/native/.
  • Need to verify that in a Managed -> NativePackage1 -> NativePackage2 graph, NuGet flows NativePackage2 to Managed.
• Zig.Sdk projects should be able to reference other Zig.Sdk projects.
  • We need to transitively pick up native libraries, include directories, and the Zig package directory.
  • If it's an executable project, we should include all dependent native libraries in the output directory, publish directory, and package.
  • A project referencing an executable project is not supported and should ideally produce an error.
• Zig.Sdk projects should be able to reference managed projects.
  • Not for runtime consumption; mainly for tooling/build purposes (i.e. ReferenceOutputAssembly=false).
  • Embedding/hosting scenarios are very out of scope (for now, at least).
• Zig.Sdk projects should be able to reference managed packages.
  • Not for runtime consumption; mainly for tooling/build purposes (e.g. Nerdbank.GitVersioning).
  • This should already Just Work, but needs testing in a sample project.
• Zig.Sdk projects should be able to reference Zig.Sdk packages.
  • We need to pick up native libraries (runtimes/<rid>/native/), include directory (include/), and Zig package directory (zig/).
    • These also need to flow transitively to dependents.
  • No special logic for executables (tools/<rid>/native/ in the package).

Notes:

• Managed -> Zig.Sdk project references will need to use this pattern.
• Giving a helpful error for project reference cycles would be nice, but isn't essential.

[alexrp]

Part of this work is going to be blocked by https://github.com/dotnet/runtime/issues/54645.

[alexrp]

This is going to depend on ziglang/zig#9251 ziglang/zig#9347. Hopefully it (in some form) can be included in Zig 0.8.1.