Add the testharness service to sepolicy rules

The testharness service will manage Test Harness Mode and provide a
command-line interface for users to enable Test Harness Mode; however it
does not directly provide a public API.

Bug: 80137798
Test: make
Test: flash crosshatch
Change-Id: Ie396e40fcea8914b4dd2247f2314e029b66ad84e
diff --git a/private/app.te b/private/app.te
index 876406f..4e433eb 100644
--- a/private/app.te
+++ b/private/app.te
@@ -10,6 +10,10 @@
 # info etc.
 allow appdomain priv_app_tmpfs:file read;
 
+# Allow apps to read the Test Harness Mode property. This property is used in
+# the implementation of ActivityManager.isDeviceInTestHarnessMode()
+get_prop(appdomain, test_harness_prop)
+
 neverallow appdomain system_server:udp_socket {
         accept append bind create ioctl listen lock name_bind
         relabelfrom relabelto setattr shutdown };