Add SELinux policy for Conscrypt APEX

Bug: 110404540
Test: cts -m CtsLibcoreTestCases -t com.android.org.conscrypt
Change-Id: Id89fc0f5e39515093f1d9d8a4fd075d717b50cf8

apex/com.android.conscrypt-file_contexts

+#############################
+# System files
+#
+(/.*)?                   u:object_r:system_file:s0
+/lib(64)?(/.*)?          u:object_r:system_lib_file:s0