Add rust_test and update TEST_MAPPING am: 99abb8cc83 am: 52e038d115 am: 579c369b07 am: 73820cf734

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/futures-util/+/1366083

Change-Id: I2d2cf46ffbe9333bc975166ede7fae4985c7fa3e