Use VCPKG to maintain dependencies

[fruffy]

Dependency installation currently takes up the majority of CI time. We could possibly speed this up using a modern package manager. vcpkg and cmake seem to be a popular combination. We should consider it.

This could also be a GSoC project.

[vgurevich]

@fruffy -- you might want to look at this project, that uses NIX to manage SDE dependencies.

If you do have access, you can read the full thread here.

@alexandergall has a lot of experience working with the SDE and is very helpful.

[alexandergall]

@vgurevich thanks for the mention. I'm currently working on porting the Nix packaging from the Intel SDE to open-p4studio. That includes separate packaging of p4c. So in my build, I don't use the p4c submodule in open-p4studio but use a pre-built p4c as a dependency of open-p4studio. This also relates to p4lang/project-ideas#22. Note that Nix completely decouples the build from the native package manager, i.e. there would be no restrictions on the Linux distribution used by the build host.

To take advantage of that for CI, it would be worth looking at Nix' own CI system called Hydra (https://hydra.nixos.org/build/290086623/download/1/hydra/). It would allow to create build environments in a deterministic and efficient manner. Hydra is used to build the Nixpkgs collection itself: https://hydra.nixos.org/.