Generate apex_available from c2a instead of a patch am: 9d0e2785f6 am: a2a05c87b5

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

Change-Id: I1d86fefa03970b4b1e0ec9bcea6d09e200f7f8ad