Add method for reading VmRSS from status am: 0f208eb2aa am: 8f09e4fb78

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

Change-Id: Id35852fbe4105fefa08f3d324d287591e642bbdf
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>