Import source for the indexmap. am: d57d0b2951

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/indexmap/+/2160336

Change-Id: If0808e8fe3c6579b3f933663a431b4bb067f52e2
Signed-off-by: Automerger Merge Worker <[email protected]>