Import async-stream-impl v0.3.0 am: 4d90486f87

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/async-stream-impl/+/1594011

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: I8002c7ce66c472f5cae52df7a56d7c98e787c15e