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

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

Change-Id: Ie162694c83865459959bfcf90a6e4058d1f1c7de
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>