Add method for reading VmRSS from status am: 0f208eb2aa

Original change: https://android-review.googlesource.com/c/platform/system/memory/libmeminfo/+/2741414

Change-Id: Id1b5805b82797ae665f284f4ce76c8a7f233408c
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>