ReadDecorHandleKey: Fix for updated parent container name.
As @fwinkl pointed out, the ReadDecorHandlKey
has the same bug that MR !64118 (merged) fixed for the WriteDecorHandleKey. This MR applies the same code-change to ReadDecorHandleKey.icc
At the same time, extend the existing unit-tests to cover the case of a parent-container key being updated before initialize()