Add flag to R8 wrapper to enable optimizing resource shrinking am: ee4be74e62

Original change: https://android-review.googlesource.com/c/platform/prebuilts/r8/+/2966687

Change-Id: Ia838a6ca70d3e2b995e16805733e096fde3f9ec5
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>