feat: follow symlinks in dependency graph

[keithamus]

What?

This adds a call to require.resolve within dependency-graph, as require.resolve will canonicalize any symlinks within the path, to get the fully qualified path.

Why?

This allows us to use symlinks (such as npm link or yarn workspaces) and have the dependency graph resolve to the fully qualified files on disk. Without this change the dependency graph will only read the path, where the linter will lookup and resolve the existing files, and so there becomes a mismatch. Resolving symlinks resolves the mismatch.

We could optionally avoid using require.resolve and use fs.readlink - but fs.readlink will not canonicalize paths, in other words if node_modules/foo was a symlink then fs.readlink('node_modules/foo') would resolve, but fs.readlink('node_modules/foo/bar.js') would throw (other methods like fs.readFile('node_modules/foo/bar.js') will resolve as they do canonicalise symlinks).

[koddsson]

This looks good to me but I'll leave the approval to someone else since we worked on this together.