neverallow coredomain from writing vendor properties

System properties can be abused to get around Treble requirements of
having a clean system/vendor split.  This CL seeks to prevent that by
neverallowing coredomain from writing vendor properties.

Bug: 78598545
Test: build 2017 Pixels
Test: build aosp_arm64
Change-Id: I5e06894150ba121624d753228e550ba9b81f7677
(cherry picked from commit cdb1624c)