Prevent transition to coredomain except for system files and vice versa

Add a neverallow to prevent coredomain from accessing entrypoint for
files other than system_file_type and postinstall_file.  Add the
complementary neverallow to prevent domains other than coredomain from
accessing entrypoint for files other than vendor_file_type and
init_exec (for vendor_init).

Bug: 155124994
Test: build
Change-Id: I6e0cb7fb445b96b82e434e949b59c299aee1ad8b
1 file changed