Add rust_test and update TEST_MAPPING am: 45fef2cd78 am: 09ab1d8aad am: 77daf241a1

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/regex-syntax/+/1365399

Change-Id: Ia40b2aeecdf59317087edf55eed364501214efb1