Update D8 and R8 to 8.3.18-dev am: 0760a761c6 am: ef5a1998dd

Original change: https://android-review.googlesource.com/c/platform/prebuilts/r8/+/2838660

Change-Id: Ia90047a8d1dc6dde06ab6af27d15a6781686d660
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>