cwd attribute on nodejs_binary, nodejs_test, npm_package_bin

[alexeagle]

Followup to #1840

That issue was resolved by documenting a workaround with --require
https://github.com/bazelbuild/rules_nodejs/blob/stable/internal/node/test/chdir/BUILD.bazel
but that's not really nice.

Ideally users could pass sth like cwd = "$(RULEDIR)" to run the tool in the output directory under the current package, though they still may need copy_to_bin so that the tool sees other InputArtifacts relative to the cwd.

Or they could pass cwd = native.package_name() to run in the input directory under the current package

In both cases we also need a big warning on the documentation that says that other paths you get from bazel, like arguments passed to your tool, or paramfiles with paths, are still going to be workspace-relative.