[rust] Generate a rust-project.json file for rust-analyzer

Rust-analyzer can read a rust-project.json file describing the crates in
a build instead of using Cargo.toml files. Adds build system support for
generating such a file describing all of the Rust crates in the build.

Test: build rust app and inspect rust-project.json
Bug: 196474053
Change-Id: I1b7e7e8b4bae63336b12614bd8c92b5c501986ca
1 file changed