Import async-stream v0.3.0 am: 647493e10d am: d822959c82 am: 1c21470013 am: 933a786e24

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/async-stream/+/1592880

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: Ie0a0f8fbaf3dd4951945fa8f85f2b9b20ef142ec