Add metadata files for walkdir. am: 9e26f4583b am: 3ebd2fc459 am: a37469b49d am: 741ca50114

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/walkdir/+/1622510

Change-Id: Id8b55b5495b6f351ded313da463c68461f0f8b94