Rename R8 library target and add R8 binary target. am: 414ff957ec am: b36be79579 am: feab5cf14f am: dc73296233

Original change: https://android-review.googlesource.com/c/platform/prebuilts/r8/+/2053948

Change-Id: Iaba237300e9fa92e8be775f4f66b2bf5d744eac4
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>