sepolicy: restrict /vendor/overlay from most coredomains

The change makes 'vendor_overlay_file' accessible only to few platform
domains like idmap, system_server, zygote and appdomain.

The overlay files contains RROs (runtime resource overlays)

Bug: 36681210
Test: Boot sailfish (treble device) from wiped flashall
Test: Connect to wifi and launch chrome to load few websites.
Test: Launch camera and record + playback video

Change-Id: I3596ca89ad51d0e7d78c75121f22ea71209ee332
Signed-off-by: Sandeep Patil <sspatil@google.com>