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

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

Change-Id: Ie76b034f348393ff435c9653f7954e87139bf1a0
Signed-off-by: Automerger Merge Worker <[email protected]>