This is required to publish script_bindings, since all files used during
codegen need to be there.
It might also be possible to generate the bindings ahead of time and
vendor them in-tree, but this seems painful to setup from a CI
perspective.
Since there don't seem to be any other users in-tree we can just vendor
into the script-bindings directory.
`ply` is licensed under the BSD 3 clause, and WebIDL under MPL-2.0, with
the licenses available in our cargo package. Both tools won't end up in
`servo` since they are build-time dependencies, so I believe we don't
need to adjust the crate license, or configure `about.toml`.
Testing: Should be covered by existing tests. We don't test if this
allows vendored builds or published builds.
Fixes: Partial fix for #43145
---------
Signed-off-by: Jonathan Schwender <schwenderjonathan@gmail.com>
