Make init.userspace_reboot.is_supported a rw property

General recommendation is to avoid read-only properties, and instead control
"read-onlines" by only allowing init/vendor_init to set the property.

Since ro.init.userspace_reboot.is_supported was added in this release, and
nobody outside of the platform is querying it directly, it should be fine to
simply rename it.

Test: adb shell getprop init.userspace_reboot.is_supported
Test: atest CtsUserspaceRebootHostSideTestCases
Bug: 152803929
Change-Id: I31b9ac7f2c92ce82664a0266aea62faa2bdd365f

core/java/android/os/PowerManager.java

@@ -29,6 +29,7 @@ import android.annotation.TestApi;
 import android.compat.annotation.UnsupportedAppUsage;
 import android.content.Context;
 import android.service.dreams.Sandman;
+import android.sysprop.InitProperties;
 import android.util.ArrayMap;
 import android.util.Log;
 import android.util.proto.ProtoOutputStream;
@@ -1336,7 +1337,7 @@ public final class PowerManager {
      */
     // TODO(b/138605180): add link to documentation once it's ready.
     public boolean isRebootingUserspaceSupported() {
-        return SystemProperties.getBoolean("ro.init.userspace_reboot.is_supported", false);
+        return InitProperties.is_userspace_reboot_supported().orElse(false);
     }
 
     /**