Android 12.0.0 release 18
Generate apex_available from c2a instead of a patch am: 9d0e2785f6 am: a2a05c87b5 am: 0fc74f4358

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/proc-macro-nested/+/1689358

Change-Id: Ib9908aad194b4412676220e65dbe670eacc5a3ba