add privapp_allowlist property to android_app

This change allows override_android_app to use the same
privapp_allowlist as the non-override module so that they will always
remain in sync.

Test: go test ./java -v -run TestPrivappAllowlist
Test: go test ./apex -v -run TestApexWithApps
Test: m com.android.permission com.google.android.permission and verify
  manually that apex_payload.img contains correct privapp_allowlist
Test: m com.android.permission before and after change &&
  `diffoscope apex_payload_reference.img apex_payload_with_change.img`
  && verify that there are no semantic changes
Bug: 242509786
Change-Id: Ifdcb28af40763aed7a4aac9a7f681153554bc256