Merge "Unhide some methods in java.util.concurrent.CompletableFuture" am: 0934b9e8b4

Original change: https://android-review.googlesource.com/c/platform/libcore/+/1596574

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: I885b507756c2f7d4cccabc9948b1d4347a99ed19