Add rust_test and update TEST_MAPPING am: ad5b93b26c am: 71c283f243 am: 3bfefd5d00

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/unicode-width/+/1365107

Change-Id: I56d929b7ddd0487e6e19b8c6910db0ceefa4ca80