This is indeed missing, try adding:
DGNPLATFORM_TYPEDEFS (TemplateSymbologyRemapper)
...before including MstnElementTemplate.h to work around the omission. This will create a typedef for TemplateSymbologyRemapperP. If you are looking to call one of the methods that takes this arg, you can pass nullptr to get the default behavior (which is what you want anyway).
-B
DGNPLATFORM_TYPEDEFS (TemplateSymbologyRemapper)
...before including MstnElementTemplate.h to work around the omission. This will create a typedef for TemplateSymbologyRemapperP. If you are looking to call one of the methods that takes this arg, you can pass nullptr to get the default behavior (which is what you want anyway).
-B