Emit lockfile v2 and fix bin links with NPM v7+

[lilyinstarlight]

Lockfile v2 mostly just has a bit of extra metadata and all dependencies are hoisted to the top-level with path-specific keys in a new lock value called "packages". This update emits enough of the format that NPM v7+ seem to be happy enough with it and does not try to rewrite it and cause ENOTCACHED errors with the sandbox.

As of NPM v7+, it no longer links bins for the top-level project automatically unless a global install is selected¹ (and is not a problem specific to node2nix²). Given a global install would cause more problems than it would solve, I added a simple script to perform the linking ourselves and instructed npm install to never link them for consistency.

Additionally, this adds a postRebuild hook that can be used by packages to run extra build scripts as needed by the project before the npm install step prunes dev dependencies (also seems to be a new behavior of NPM v7+, but admittedly this behavior could be due to the fake lock file confusing it a little)

Closes #236, closes #293, closes #294

Edit: Marking as draft until I can get this to work completely with the nodePackages attrset in nixpkgs

[lilyinstarlight]

Okay, I think I've got this rebuilding the nodePackages attrset without regressions with Node.js 18 (after fixing a few specific packages that hadn't been rebuilding properly before the update but still "built")

This should be ready for review/merge and I will be making a companion PR in nixpkgs in a few that brings the nodePackages attrset up to using the latest LTS rather than being pinned to nodejs-14_x

[lilyinstarlight]

Opened PR in nixpkgs as NixOS/nixpkgs#193337

[svanderburg]

Ok, nice contribution! I'll merge it

[CMCDragonkai]

What version of node2nix is coming out as?