Import protobuf-json-mapping crate. am: bb8920e11b am: daeeea76da am: 52c5d139a8

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/protobuf-json-mapping/+/2514115

Change-Id: If45ac419ec428fcd3406d735967118b57cf77016
Signed-off-by: Automerger Merge Worker <[email protected]>