Fix bug in parser while trying to use IL operator like S1, R1, etc... as standard function block interface variable in structured_variable syntax and bug in code generator while generating code for assignment of function block interface variable using structured_variable syntax

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