Merge "Default to Android prebuilt Rust toolchain rather than local toolchain." into main am: 26c05cc107 am: bd1387fae6

Original change: https://android-review.googlesource.com/c/platform/development/+/2796405

Change-Id: I49497ef829e2918fb67354a0115fbc8c9bb698b0
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>