Make crate vendor_available, use public header am: 2e4b28ef02 am: c213cb93db am: bc7be13165 am: f3bd7488b6 am: 6596184ec7

Original change: https://android-review.googlesource.com/c/platform/system/librustutils/+/2104868

Change-Id: I24ae57ceb430d0558ff14ba746dc809d84bba90b
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>