Merge "Add function for flattening 2d lists" am: 8ccac519 am: 6d0c689c

Original change: https://android-review.googlesource.com/c/platform/build/+/2088663



Change-Id: I9b68e862c17241f558ccca8c1a931613aa464c61
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>