Add a persist.wm.debug property type and associated permissions

This is intended for wm properties related to wmshell/sysui.
Using this context allows sysui to manipulate these properties
in debug builds.

Bug: 219067621
Test: manual
Change-Id: I5808bf92dbba37e9e6da5559f8e0a5fdac016bf3
diff --git a/private/system_server.te b/private/system_server.te
index 682be60..275bb6f 100644
--- a/private/system_server.te
+++ b/private/system_server.te
@@ -799,6 +799,9 @@
 # Read hypervisor capabilities ro.boot.hypervisor.*
 get_prop(system_server, hypervisor_prop)
 
+# Read persist.wm.debug. properties
+get_prop(system_server, persist_wm_debug_prop)
+
 # Create a socket for connections from debuggerd.
 allow system_server system_ndebug_socket:sock_file create_file_perms;