Initial import of cast-0.2.3. am: 80f5cd0831 am: 46353a3021 am: f8edbc5cc4 am: ab700367e7

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/cast/+/1620970

Change-Id: I53797effda716124e6b433eb4c232f1d96725fa7