Make generate_workspace dump transitive dependencies for Maven artifacts
Make generate_workspace dump transitive dependencies for Maven artifacts

This moves the WORKSPACE-parsing code out of WorkspaceFileFunction.java so
generate_workspace can parse a WORKSPACE into an ExternalPackage without having
to muck with Skyframe.

Addresses issue #89.

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MOS_MIGRATED_REVID=96777708

davidzchen/bazel-website,davidzchen/bazel-website,bazelbuild/bazel-website,bazelbuild/bazel-website,davidzchen/bazel-website,bazelbuild/bazel-website,davidzchen/bazel-website