This service is used to resolve references from MPlaceholders.
The issue is that we may be storing a cloned snippet which contains references to 'shared
elements' but instantiating the snippet in a new window requires that the shared elements list be
This interface is not intended to be referenced by clients.
This method is used to re-resolve a placeholder's reference to a 'shared part' within the
context of a particular window. This is necessary because placeholders must be referencing an
element in that window's 'sharedParts' list.
Implementors may presume that the if the placeholder's reference is already non-null then it
has already been resolved.
ph - The placeholder to set the reference for (if necessary)
refWin - The window the whose shared parts are to be referenced