Add a new node to the abstract symtax tree, which will let us do datatype checking of FB variable declarations using the standard algorithm, and no special cases.

STD_TEST.st
STD_RESSOURCE.c
LOCATED_VARIABLES.h
POUS.c
test
STD_CONF.c
SFC_TEST.st
test.exe
plc.st
POUS.h
VARIABLES.csv