libloading: make libloading vendor available. am: e5afd9f6aa am: 89b02bcdf5 am: 4e06fcb867 am: 291268512c

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/libloading/+/2457728

Change-Id: I4f723c2324be9ddb8f3b0985a617a70b9b445eb4
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>