[automerge] Add a runtime check to ensure that system server jars are prefetched. 2p: 418ab8212c 2p: 1cab79eff5

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/16970524

Bug: 203198541
Change-Id: Ic65c70822e2282b5117b1a8d61f11b15c9ed7904