Reland "Enable R8 full mode by default for apps"

This is attempt 3 at landing this change. Prior attempts were
reverted due to downstream test breakages not in presubmit.
Those issues have been resolved, and additional manual heavy
presubmit tests were run to ensure stability.

Observed APK savings: ~24MB

This reverts commit a2ab9366.

Reason for revert: Fixed SdkSandboxManagerTest by preserving
existing R8 compat mode for the aosp variant of SdkSandbox target.

Bug: 215530220
Bug: 293177283
Test: atest SdkSandboxManagerTests && \
      atest SdkSandboxStorageHostTest && \
      atest SdkSandboxLifecycleHostTest

Change-Id: If5636638875b6f67e0cc0ba4fd253a8d99d8db1d