Public HPKE API. am: 89a46d5584 am: 030236d1c3

Original change: https://android-review.googlesource.com/c/platform/art/+/2967375

Change-Id: I551bfe6570b3f8e0e727a83a42c5043322927e10
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>