Add rust_test and update TEST_MAPPING am: a944bcbf53 am: 6ca23e872e am: d8507ce348

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/futures-core/+/1365564

Change-Id: I9c1001cce286752ca8cf6d4951f49ed1606f6671