LPS-33811 Adding new helper methods to PortletDataContext - since the portlet and staged model data handlers both use these helpers, it made sense to put in here in a centralized place
LPS-33811 Remove element typed parameters from interface and base staged model data handler class
LPS-33811 Apply change to Bookmarks first as an example
LPS-33811 Apply similar pattern to the rest of the StagedModelDataHandlers
LPS-33811 Apply changes to the portlet data handlers according to the StagedModelDataHandler changes
LPS-33811 Apply changes to the base test case accordingly
LPS-33811 Cleaning up unnecessary methods in StagedModelDataHandler integration tests
LPS-33811 Apply base test logic changes to actual test classes