Copy API 28 artifacts to new directory structure.

Like aosp/667922, but for the newly finalized API 28. Steps taken:
$ mkdir -p 28/public/api 28/system/api
$ cp 28/android.jar 28/framework.aidl 28/uiautomator.jar 28/optional/*.jar 28/public
$ cp api/28.txt 28/public/api/android.txt
$ cp system_28/android.jar system_28/framework.aidl 28/system
$ cp system-api/28.txt 28/system/api/android.txt

I will be repeating this process if the 28 artifacts change.

Bug: 77525052
Test: Currently unused, tested in follow-up make changes.
Change-Id: I736cd36f0f3ad46c88f65541f4a58d5bd7c8efac
10 files changed