Add rust_test and update TEST_MAPPING am: 45fef2cd78 am: 09ab1d8aad am: 77daf241a1 am: d8d370b0de

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

Change-Id: I21bbc6f184a90bdf8c36b185d75451ac5bc03bbb