Reland "Treat input files as public API."

Input files are public API:
https://source.android.com/devices/input/input-device-configuration-files
Now that they have labels from core policy (aosp/782082), we can tighten
up our neverallows.

Bug: 37168747
Test: m selinux_policy
Change-Id: Ifaf9547993eb8c701fb63b7ee41971ea4e3f7cf9