Android 12.0.0 release 20
Generate apex_available from c2a instead of a patch am: 6e21a92345 am: b9ecefff4f am: 33e398951a

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/futures/+/1688688

Change-Id: I3e828bb84b6f3b12bc191e2a1c0c198d59746390