Android 12.0.0 release 19
Generate apex_available from c2a instead of a patch am: a8fea1d912 am: 9b2d6414ab am: 84aa6e7a64

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/futures-channel/+/1688765

Change-Id: Id2c337116df5e3861dff0e50756125bd4bbaafb1