Improve neverallows on /proc and /sys

Access to these files was removed in Oreo. Enforce that access is not
granted by partners via neverallow rule.

Also disallow most untrusted app access to net.dns.* properties.

Bug: 77225170
Test: system/sepolicy/tools/build_policies.sh
Change-Id: I85b634af509203393dd2d9311ab5d30c65f157c1