[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.py
Bug: 196474053
Change-Id: I295d04c3f06e438635957469c5683f1159ef0faf
1 file changed