Add virtualizationservice.state.last_cid

It is a system property that keeps the last CID used by the
virtualizationservice. Although the information is local to the
process, a new system property is justified because the information has
to be kept across multiple runs of the process. A file however is not
desirable because the information shouldn't be persisted.

Bug: 196015427
Test: atest MicrodroidHostTestCases
Change-Id: If8ca4b6ad8d9c8cb3bb33dc9ef45de0ae6481d15

private/property.te

@@ -40,6 +40,7 @@ system_internal_prop(verity_status_prop)
 system_internal_prop(zygote_wrap_prop)
 system_internal_prop(ctl_mediatranscoding_prop)
 system_internal_prop(ctl_odsign_prop)
+system_internal_prop(virtualizationservice_prop)
 
 ###
 ### Neverallow rules

private/property_contexts

@@ -1233,3 +1233,6 @@ ro.bootanim.quiescent.enabled u:object_r:bootanim_config_prop:s0 exact bool
 
 # dck properties
 ro.gms.dck.eligible_wcc u:object_r:dck_prop:s0 exact int
+
+# virtualization service properties
+virtualizationservice.state.last_cid u:object_r:virtualizationservice_prop:s0 exact uint

private/virtualizationservice.te

@@ -54,3 +54,11 @@ allow virtualizationservice staging_data_file:file r_file_perms;
 
 # Let virtualizationservice to accept vsock connection from the guest VMs
 allow virtualizationservice self:vsock_socket { create_socket_perms_no_ioctl listen accept };
+
+# Allow virtualizationservice to read/write its own sysprop. Only the process can do so.
+set_prop(virtualizationservice, virtualizationservice_prop)
+neverallow {
+  domain
+  -init
+  -virtualizationservice
+} virtualizationservice_prop:property_service set;