- We're moving from `depends_on "python-lxml"` to `resource "lxml" ...` as part
of the new Python vendoring plan.
- For `resource "lxml"` to work, `uses_from_macos "libxml2"` and
`uses_from_macos "libxslt"` are needed in the formulae.
- This new RuboCop rule enforces that a formula including the "lxml" resource
also include those dependencies.