Add support for binary-only crates with crate_universe

[adsnaider]

The documentation specifies that crate_universe doesn't support binary-only dependencies out of the box: http://bazelbuild.github.io/rules_rust/crate_universe.html#binary-dependencies. It would be really nice if it did. How much work would it be to implement? I would be happy to try contributing this feature.

[illicitonion]

If we're going to support this, it would likely be via #1739 (see also #2031).

I expect it's probably a relatively small amount of work to do, but it's using an unstable cargo feature so you may run into bugs on the way (and will also need to fork the cargo_metadata crate to modify some structs in there) :)

[mikea]

this limitation is very painful with cxxbridge-cmd. I see quite a few projects on github (google's skia including) trying to implement the workaround.

[UebelAndre]

this limitation is very painful with cxxbridge-cmd. I see quite a few projects on github (google's skia including) trying to implement the workaround.

There are some known work-arounds. The wasm_bindgen_library rule uses one of them. If anyone is willing to try out nightly releases of Rust (Cargo) that support -zbindeps I'd be happy to review pull-requests to make any updates needed for crate_universe to parse the new info from cargo metadata (since that's the source of truth crate_universe uses to generate dependencies).