Re-added Property.toString warning messages (#10916)

* Made it possible to toggle the toString() behavior using the "legacyPropertyToString" init parameter. The default value is "warning" which enables the legacy Property.toString implementation and logs a warning message when it is used. Other supported values are "true" which enables the legacy mode and "false" which disables it.

Change-Id: Ife19352b86590464c8e441b7f82f4fec3b1f3235