Allow priv apps MANAGE_VIRTUAL_MACHINE permission

Also add comments to all our various permissions.

Bug: 255286871
Test: Install demo app to system/priv-app, see it work without explicit grant.
Change-Id: I05c89e533b9cb11148cfc477dd25a1f3db5bd9ca
diff --git a/javalib/Android.bp b/javalib/Android.bp
index a6c3b80..51dd381 100644
--- a/javalib/Android.bp
+++ b/javalib/Android.bp
@@ -7,7 +7,7 @@
     name: "android.system.virtualmachine.res",
     installable: true,
     apex_available: ["com.android.virt"],
-    sdk_version: "current",
+    platform_apis: true,
 }
 
 java_sdk_library {