Merge "Add String16::c_str and start using it." into main am: 067dbcc1

Original change: https://android-review.googlesource.com/c/platform/system/core/+/2704555



Change-Id: I5e9a0c633b67038cedbe2144f5f0c479c8de9e0b
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>