expand the ListLoop macros

Following discussions with Leopold and @sbna, makes sense to unbox the List_FOR_ALL macro into its constituent parts.

As it stands, cannot place an loop pragmas in front, since there is an embedded initial looping parameter. Cannot easily embed an _Pragma() within the macro since a macro paste token (_n##i) is used.

Main use case are the TFOR_ALL... macros in FieldM.H (used for various list/field operations). So replace there with explicit, identifiable loops.