Add metadata files for either. am: 27f5168c66 am: 7ca9b7c31e am: 506d75e22c am: 85f89ad7f8

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/either/+/1621404

Change-Id: I4faddd6db3d80b8d3ba9eea38af900ac209995eb