Merge "libdm: Export ExtractBlockDeviceName()" into sc-dev am: de0cc6cc59 am: b155a9a8a1

Original change: https://googleplex-android-review.googlesource.com/c/platform/system/core/+/15584613

Change-Id: Ib5046e3855f5c4249eed9676022a77aa93a1adce